buck2/github: use faster Windows runners

Summary:
For some reason Cargo builds are at least twice slower on Windows than on Linux or MacOS on Github. I checked this is true for other popular Rust projects as well.

We can use faster 8-core runners instead of 2-core to reduce this difference.

Differential Revision: D66011530

.github/workflows/build-and-test.yml

@@ -21,7 +21,7 @@ jobs:
     - uses: ./.github/actions/build_debug
     - uses: ./.github/actions/run_test_py
   windows-build-and-test:
-    runs-on: windows-latest
+    runs-on: windows-8-core
     steps:
     - uses: actions/[email protected]
     - uses: ./.github/actions/setup_windows_env
@@ -72,7 +72,7 @@ jobs:
     - uses: ./.github/actions/setup_reindeer
     - uses: ./.github/actions/build_bootstrap
   windows-build-examples:
-    runs-on: windows-latest
+    runs-on: windows-8-core
     steps:
       - uses: actions/[email protected]
       - uses: ./.github/actions/setup_windows_env