Windows tar cannot overwrite read-only files

Describe the bug
C:\Windows\System32\tar.exe fails when an archive extraction needs to overwrite existing files with the read-only attribute. This creates problems in the cache action: https://github.com/actions/cache/issues/198

To Reproduce
Trigger this GitHub workflow two times:

on: push

jobs:
  test:
    runs-on: windows-latest
    steps:

      - uses: actions/checkout@v2

      - name: List read-only files
        run: Get-ChildItem .git -Recurse -Attributes ReadOnly

      - uses: actions/cache@v2
        with:
          key: break-me
          path: .git

The cache action fails on the second run, with tar reporting "Can't unlink already-existing object" errors referring to the read-only files.

Expected behavior

On the second run, the cache action should restore from the key with no errors.

Additional context
The system tar is selected in preference to GNU tar, which works as expected when --force-local option is used. GNU tar is installed in the Windows virtual environment as part of the Git toolkit and its full path name is "C:\Program Files\Git\usr\bin\tar.exe".

Start with packages/cache/src/internal/tar.ts, especially the system-tar preference, then reproduce the provided Windows workflow twice on windows-latest. Compare the system tar and GNU tar behavior described in the issue; done means the second cache restore completes without "Can't unlink already-existing object" errors when read-only files are present.