Try removing Git for Windows PATH directories

In the `test-fast` Windows jobs, this removes descendant
directories under the directory where Git for Windows is installed
on CI Windows runners, from the `PATH` environment variable. This
is done after the full test suite run.

The idea is to support running some specific tests, where
`gix-path` will have to find `git` by checking common locations.
But this does rerun any tests yet.

The other change this makes is to remove the CI runner PATH
search instrumentation steps in `test-fast` and
`test-fixtures-windows` that were just previously added. (Those
steps were added temporarily to examine how this change should be
made, and they are no longer needed.)

Author: EliahKagan

.github/workflows/ci.yml

@@ -220,12 +220,6 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-      - name: Show PATH
-        if: startsWith(matrix.os, 'windows')
-        run: $Env:PATH -split ';'
-      - name: Find git
-        if: startsWith(matrix.os, 'windows')
-        run: where.exe git
       - uses: actions/checkout@v4
       - name: Install rustup
         if: matrix.os == 'windows-11-arm'
@@ -244,6 +238,17 @@ jobs:
         run: cargo nextest run --workspace --no-fail-fast -- ${{ matrix.test-args }}
       - name: Check that tracked archives are up to date
         run: git diff --exit-code  # If this fails, the fix is usually to commit a regenerated archive.
+      - name: Remove Git for Windows directories from PATH
+        if: startsWith(matrix.os, 'windows')
+        run: |
+          $prefix = 'C:\Program Files\Git'
+          $filtered = ($Env:PATH -split ';' | Where-Object { $_ -notlike "$prefix\*" }) -join ';'
+          Add-Content -Value "PATH=$filtered" -Path $Env:GITHUB_ENV
+      - name: Check that `git` is no longer found
+        if: startsWith(matrix.os, 'windows')
+        run: |
+          $git = Get-Command git -ErrorAction SilentlyContinue
+          if ($null -eq $git) { exit 0 } else { exit 1 }
 
   test-fixtures-windows:
     strategy:
@@ -259,12 +264,6 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-      - name: Show PATH
-        if: startsWith(matrix.os, 'windows')
-        run: $Env:PATH -split ';'
-      - name: Find git
-        if: startsWith(matrix.os, 'windows')
-        run: where.exe git
       - name: Report version/build of Git in this runner image
         run: git version --build-options
       - name: Upgrade Git for Windows to latest stable release