[CI] Enable sccache GCS on premerge

This patch enables sccache using GCS for premerge.

Author: boomanaiden154

.github/workflows/premerge.yaml

@@ -62,6 +62,12 @@ jobs:
           export CC=/opt/llvm/bin/clang
           export CXX=/opt/llvm/bin/clang++
 
+          # This environment variable is passes into the container through the
+          # runner pod definition. This differs between our two clusters which
+          # why we do not hardcode it.
+          export SCCACHE_GCS_BUCKET=$CACHE_GCS_BUCKET
+          export SCCACHE_GCS_RW_MODE=READ_WRITE
+
           ./.ci/monolithic-linux.sh "${projects_to_build}" "${project_check_targets}" "${runtimes_to_build}" "${runtimes_check_targets}" "${runtimes_check_targets_needs_reconfig}" "${enable_cir}"
       - name: Upload Artifacts
         if: '!cancelled()'
@@ -113,7 +119,9 @@ jobs:
         shell: cmd
         run: |
           call C:\\BuildTools\\Common7\\Tools\\VsDevCmd.bat -arch=amd64 -host_arch=amd64
-          bash .ci/monolithic-windows.sh "${{ steps.vars.outputs.windows-projects }}" "${{ steps.vars.outputs.windows-check-targets }}"
+          bash "export SCCACHE_GCS_BUCKET=$CACHE_GCS_BUCKET; \
+          export SCCACHE_GCS_RW_MODE=READ_WRITE; \
+          .ci/monolithic-windows.sh \"${{ steps.vars.outputs.windows-projects }}\" \"${{ steps.vars.outputs.windows-check-targets }}\""
       - name: Upload Artifacts
         if: '!cancelled()'
         uses: actions/upload-artifact@65c4c4a1ddee5b72f698fdd19549f0f0fb45cf08 # v4.6.0