Add fork of checkout action with enhanced capabilities (#7597)

This is a fork of the [`actions/checkout`
action](https://github.com/actions/checkout).
The main addition is the ability to apply filters to submodule handling
and the ability to do single branch checkouts also for non-shallow
checkouts.
For this, it adds the `single-branch` and `submodules-filter` option as
described in the Usage section of the updated README.md.

The purpose is to use these extensions to cut down on checkout time in
the multitude of ci jobs that need to check out the pytorch repository
as discussed in pytorch/pytorch#169184.

The updated README.md file also includes instructions for future updates
to newer versions of the upstream action.

Some timings are taken from
pytorch/pytorch#167737:

|Workflow|Time on `viable/strict`|Time here|Time Saving|
|-|-|-|-|
|Lint/lintrunner-noclang| 2m42s | 55s | 1m47s |
| linux-jammy-py3.14-clang12/build (via _linux-build)| 2m30s | 1m29s|
61s|
| linux-jammy-cuda12.8-cudnn9-py3.10-clang12 / build (via _linux-build)
| 2m31s | 1m33s| 59s|

In other words, we can save ~1m per checkout where shallow checkouts are
not feasible, which includes build and test jobs on trunk and pull.

With a total of 276 jobs on trunk at the moment and ~90 jobs on a pull
request, assuming ~70 PRs per day, the cumulative savings with savings
of 1 minute per checkout could be between 75 and 150 hours.

---------

Co-authored-by: actions/checkout contributors <unknown@example.com>

Author: zklaus

.github/actions/checkout/.eslintignore

@@ -0,0 +1,3 @@
+dist/
+lib/
+node_modules/

.github/actions/checkout/.eslintrc.json

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+{
+  "plugins": ["jest", "@typescript-eslint"],
+  "extends": ["plugin:github/recommended"],
+  "parser": "@typescript-eslint/parser",
+  "parserOptions": {
+    "ecmaVersion": 9,
+    "sourceType": "module",
+    "project": "./tsconfig.json"
+  },
+  "rules": {
+    "eslint-comments/no-use": "off",
+    "import/no-namespace": "off",
+    "no-unused-vars": "off",
+    "@typescript-eslint/no-unused-vars": "error",
+    "@typescript-eslint/explicit-member-accessibility": ["error", {"accessibility": "no-public"}],
+    "@typescript-eslint/no-require-imports": "error",
+    "@typescript-eslint/array-type": "error",
+    "@typescript-eslint/await-thenable": "error",
+    "camelcase": "off",
+    "@typescript-eslint/explicit-function-return-type": ["error", {"allowExpressions": true}],
+    "@typescript-eslint/func-call-spacing": ["error", "never"],
+    "@typescript-eslint/no-array-constructor": "error",
+    "@typescript-eslint/no-empty-interface": "error",
+    "@typescript-eslint/no-explicit-any": "error",
+    "@typescript-eslint/no-extraneous-class": "error",
+    "@typescript-eslint/no-floating-promises": "error",
+    "@typescript-eslint/no-for-in-array": "error",
+    "@typescript-eslint/no-inferrable-types": "error",
+    "@typescript-eslint/no-misused-new": "error",
+    "@typescript-eslint/no-namespace": "error",
+    "@typescript-eslint/no-non-null-assertion": "warn",
+    "@typescript-eslint/no-unnecessary-qualifier": "error",
+    "@typescript-eslint/no-unnecessary-type-assertion": "error",
+    "@typescript-eslint/no-useless-constructor": "error",
+    "@typescript-eslint/no-var-requires": "error",
+    "@typescript-eslint/prefer-for-of": "warn",
+    "@typescript-eslint/prefer-function-type": "warn",
+    "@typescript-eslint/prefer-includes": "error",
+    "@typescript-eslint/prefer-string-starts-ends-with": "error",
+    "@typescript-eslint/promise-function-async": "error",
+    "@typescript-eslint/require-array-sort-compare": "error",
+    "@typescript-eslint/restrict-plus-operands": "error",
+    "semi": "off",
+    "@typescript-eslint/semi": ["error", "never"],
+    "@typescript-eslint/type-annotation-spacing": "error",
+    "@typescript-eslint/unbound-method": "error"
+  },
+  "env": {
+    "node": true,
+    "es6": true,
+    "jest/globals": true
+  }
+}

.github/actions/checkout/.gitattributes

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+.licenses/** -diff linguist-generated=true

.github/actions/checkout/.gitignore

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+__test__/_temp
+_temp/
+lib/
+node_modules/
+.vscode/

.github/actions/checkout/.licensed.yml

@@ -0,0 +1,18 @@
+name: "Checkout Action"
+
+root: .
+
+sources:
+  npm: true
+
+allowed:
+  - apache-2.0
+  - bsd-2-clause
+  - bsd-3-clause
+  - isc
+  - mit
+  - cc0-1.0
+  - unlicense
+
+reviewed:
+  npm: