Repair cached Python directory junctions on Windows (#1122)

With `cache-python: true`, a Windows runner can report a cache hit while
extracting the cache incorrectly. When `@actions/cache`'s tar extracts
uv's minor-version junction before the patch directory it points to, it
creates a file symlink. Resolving that link later raises `[WinError 5]
Access is denied`.

This PR fixes things up after restoring the Python cache, recreating the
junction if resolving the link fails with access denied and its recorded
target is a matching, accessible CPython installation in the same
directory.

This is a temporary workaround until
https://github.com/actions/toolkit/issues/2562 gets resolved and
`@actions/cache` itself becomes resilient to these situations.

I tested this by restoring the same archive on two fresh `windows-2022`
runners. The original run passed because resolving the minor-version
link raised the expected WinError 5. With the patch, `uv sync --offline
--managed-python --no-python-downloads` created a virtual environment
whose `home` in `pyvenv.cfg` resolved to the cached CPython 3.10.22
installation. [Original
run](https://github.com/astral-sh/ruff/actions/runs/41469344610/job/125358623949#step:9:1)
· [Patched
run](https://github.com/astral-sh/ruff/actions/runs/41469344610/job/125358623835#step:10:1).

.github/workflows/test.yml

@@ -985,14 +985,18 @@ jobs:
         run: rm -rf "$UV_PYTHON_INSTALL_DIR"
 
   test-cache-python-installs:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-2022]
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
       - name: Verify Python install dir is not populated
+        shell: bash
         run: |
-          if [ -d /home/runner/work/_temp/uv-python-dir ]; then
+          if [ -e "$RUNNER_TEMP/uv-python-dir" ]; then
             echo "Python install dir should not exist"
             exit 1
           fi
@@ -1005,21 +1009,26 @@ jobs:
       - run: uv sync --managed-python
         working-directory: __tests__/fixtures/uv-project
       - name: Verify Python install dir exists
+        shell: bash
         run: |
-          if [ ! -d /home/runner/work/_temp/uv-python-dir ]; then
+          if [ ! -d "$UV_PYTHON_INSTALL_DIR" ]; then
             echo "Python install dir should exist"
             exit 1
           fi
   test-restore-python-installs:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
     needs: test-cache-python-installs
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-2022]
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
       - name: Verify Python install dir does not exist
+        shell: bash
         run: |
-          if [ -d /home/runner/work/_temp/uv-python-dir ]; then
+          if [ -e "$RUNNER_TEMP/uv-python-dir" ]; then
             echo "Python install dir should not exist"
             exit 1
           fi
@@ -1030,19 +1039,21 @@ jobs:
           enable-cache: true
           cache-python: true
           cache-suffix: ${{ github.run_id }}-${{ github.run_attempt }}-test-cache-python-installs
-      - name: Verify Python install dir exists
-        run: |
-          if [ ! -d /home/runner/work/_temp/uv-python-dir ]; then
-            echo "Python install dir should exist"
-            exit 1
-          fi
-      - name: Cache was hit
-        run: |
-          if [ "$CACHE_HIT" != "true" ]; then
-            exit 1
-          fi
+      - name: Verify the restored Python minor-version link resolves to the patch directory
+        shell: python
         env:
           CACHE_HIT: ${{ steps.restore.outputs.python-cache-hit }}
+        run: |
+          import os
+          from pathlib import Path
+
+          assert os.environ["CACHE_HIT"] == "true", "expected a Python cache hit"
+          installs = Path(os.environ["UV_PYTHON_INSTALL_DIR"]).resolve()
+          assert installs.is_dir(), "Python install dir should exist"
+          patch_dir, = installs.glob("cpython-*.*.*-*")
+          minor_prefix = patch_dir.name.rsplit(".", 1)[0]
+          alias, = installs.glob(f"{minor_prefix}-*")
+          assert alias.resolve(strict=True) == patch_dir, alias
       - run: uv sync --managed-python
         working-directory: __tests__/fixtures/uv-project