.github/workflows: use tailscale/go for Windows CI too

We did so for Linux and macOS already, so also do so for Windows. We
only didn't already because originally we never produced binaries for
it (due to our corp repo not needing them), and later because we had
no ./tool/go wrapper. But we have both of those things now.

Updates #18884

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

.github/workflows/test.yml

@@ -244,12 +244,6 @@ jobs:
       with:
         path: ${{ github.workspace }}/src
 
-    - name: Install Go
-      uses: actions/setup-go@4b73464bb391d4059bd26b0524d20df3927bd417 # v6.3.0
-      with:
-        go-version-file: ${{ github.workspace }}/src/go.mod
-        cache: false
-
     - name: Restore Go module cache
       uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
       with:
@@ -269,7 +263,9 @@ jobs:
     - name: test
       if: matrix.key != 'win-bench' # skip on bench builder
       working-directory: src
-      run: go run ./cmd/testwrapper sharded:${{ matrix.shard }}
+      run: ./tool/go run ./cmd/testwrapper sharded:${{ matrix.shard }}
+      env:
+        NOPWSHDEBUG: "true" # to quiet tool/gocross/gocross-wrapper.ps1 in CI
 
     - name: bench all
       if: matrix.key == 'win-bench'
@@ -277,7 +273,9 @@ jobs:
       # Don't use -bench=. -benchtime=1x.
       # Somewhere in the layers (powershell?)
       # the equals signs cause great confusion.
-      run: go test ./... -bench . -benchtime 1x -run "^$"
+      run: ./tool/go test ./... -bench . -benchtime 1x -run "^$"
+      env:
+        NOPWSHDEBUG: "true" # to quiet tool/gocross/gocross-wrapper.ps1 in CI
 
     - name: Print stats
       shell: pwsh
@@ -287,19 +285,6 @@ jobs:
       run: |
         Invoke-Expression "$env:GOCACHEPROG --stats" | jq .
 
-  win-tool-go:
-    runs-on: windows-latest
-    needs: gomod-cache
-    name: Windows (win-tool-go)
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: test-tool-go
-      working-directory: src
-      run: ./tool/go version
-
   macos:
     runs-on: macos-latest
     needs: gomod-cache