CI: Use absolute path for TYPST_FONT_PATH environment variable

This allows us to also use it in the main crate test suite.

Author: Turbo87

.github/workflows/ci.yml

@@ -206,8 +206,7 @@ jobs:
       - run: cargo test --workspace
         env:
           # Set the path to the Fira Sans font for Typst.
-          # The path is relative to the `crates_io_og_image` crate root.
-          TYPST_FONT_PATH: ../../Fira-4.202/otf
+          TYPST_FONT_PATH: ${{ github.workspace }}/Fira-4.202/otf
 
   frontend-lint:
     name: Frontend / Lint