Migrate Windows GitHub Actions CI jobs to windows-2022-8-core runners.

Upgrading from standard 4-core runners to 8-core runners speeds up cold-cache Windows CMake and Bazel builds and test runs without needing to shard test targets across multiple jobs.

Worst case CI times are now ~14m

PiperOrigin-RevId: 1010736476

.github/workflows/ci.yml

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b8a9423..03f9ea5 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -136,7 +136,7 @@
           # windows-msvc-2022-cxx17-dbg-cmake.cfg
           # windows-msvc-2022-cxx17-dbg-dll-cmake.cfg
           - name: Windows MSVC 2022
-            os: windows-2022
+            os: windows-2022-8-core
             build_types: '["Debug"]'
             link_modes: '["static", "shared"]'
     uses: ./.github/workflows/cmake.yml
@@ -170,7 +170,7 @@
     uses: ./.github/workflows/bazel.yml
     secrets: inherit
     with:
-      os: windows-2022
+      os: windows-2022-8-core
       toolchain: ${{ matrix.config.toolchain }}
       remote_config: remote-cache
       alternate_options: ${{ matrix.config.alternate_options || false }}