Create dependabot.yml and update action versions (#30)

* Create dependabot.yml

From https://discourse.julialang.org/t/psa-use-dependabot-to-update-github-actions-automatically/96001

* Update action versions

Author: abhro

.github/dependabot.yml

@@ -0,0 +1,7 @@
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/" # Location of package manifests
+    schedule:
+      interval: "weekly"

.github/workflows/ci.yml

@@ -31,46 +31,39 @@ jobs:
         arch:
           - x64
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@v2
         with:
           version: ${{ matrix.version }}
           arch: ${{ matrix.arch }}
-      - uses: actions/cache@v1
-        env:
-          cache-name: cache-artifacts
-        with:
-          path: ~/.julia/artifacts
-          key: ${{ runner.os }}-test-${{ env.cache-name }}-${{ hashFiles('**/Project.toml') }}
-          restore-keys: |
-            ${{ runner.os }}-test-${{ env.cache-name }}-
-            ${{ runner.os }}-test-
-            ${{ runner.os }}-
+      - uses: julia-actions/cache@v2
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
       - uses: julia-actions/julia-processcoverage@v1
-      - uses: codecov/codecov-action@v1
+      - uses: codecov/codecov-action@v5
         with:
-          file: lcov.info
+          files: lcov.info
+          token: ${{ secrets.CODECOV_TOKEN }}
   docs:
     name: Documentation
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@v2
         with:
           version: 'lts'
-      - run: |
-          julia --project=docs -e '
-            using Pkg
-            Pkg.develop(PackageSpec(path=pwd()))
-            Pkg.instantiate()'
-      - run: |
-          julia --project=docs -e '
-            import Documenter: doctest, DocMeta
-            using LegendrePolynomials
-            DocMeta.setdocmeta!(LegendrePolynomials, :DocTestSetup, :(using LegendrePolynomials); recursive=true)
-            doctest(LegendrePolynomials)'
+      - uses: julia-actions/cache@v2
+      - shell: julia --color=yes --project=docs {0}
+        run: |
+          using Pkg
+          Pkg.develop(PackageSpec(path=pwd()))
+          Pkg.instantiate()
+      - shell: julia --color=yes --project=docs {0}
+        run: |
+          import Documenter: doctest, DocMeta
+          using LegendrePolynomials
+          DocMeta.setdocmeta!(LegendrePolynomials, :DocTestSetup, :(using LegendrePolynomials); recursive=true)
+          doctest(LegendrePolynomials)
       - run: julia --project=docs docs/make.jl
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}