[CI][Github] Set SCCACHE_IDLE_TIMEOUT to 0 (llvm#150508)

This patch sets the sccache idle timeout to zero which ensures that it
will run indefinitely. Without this, sccache will sometimes stop when
several long test suites get run consequitively. This resets the
statistics which we save at the end. Ensuring the process stays running
means we have accurate statistics when we collect them at the end.

Author: boomanaiden154

.github/workflows/premerge.yaml

@@ -62,6 +62,12 @@ jobs:
           # why we do not hardcode it.
           export SCCACHE_GCS_BUCKET=$CACHE_GCS_BUCKET
           export SCCACHE_GCS_RW_MODE=READ_WRITE
+
+          # Set the idle timeout to zero to ensure sccache runs for the
+          # entire duration of the job. Otherwise it might stop if we run
+          # several test suites in a row and discard statistics that we want
+          # to save in the end.
+          export SCCACHE_IDLE_TIMEOUT=0
           sccache --start-server
 
           ./.ci/monolithic-linux.sh "${projects_to_build}" "${project_check_targets}" "${runtimes_to_build}" "${runtimes_check_targets}" "${runtimes_check_targets_needs_reconfig}" "${enable_cir}"
@@ -110,7 +116,9 @@ jobs:
         shell: cmd
         run: |
           call C:\\BuildTools\\Common7\\Tools\\VsDevCmd.bat -arch=amd64 -host_arch=amd64
-          bash -c "export SCCACHE_GCS_BUCKET=$CACHE_GCS_BUCKET; export SCCACHE_GCS_RW_MODE=READ_WRITE; sccache --start-server; .ci/monolithic-windows.sh \"${{ steps.vars.outputs.windows-projects }}\" \"${{ steps.vars.outputs.windows-check-targets }}\""
+          # See the comments above in the Linux job for why we define each of
+          # these environment variables.
+          bash -c "export SCCACHE_GCS_BUCKET=$CACHE_GCS_BUCKET; export SCCACHE_GCS_RW_MODE=READ_WRITE; export SCCACHE_IDLE_TIMEOUT=0; sccache --start-server; .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