[ci] Use different emoji for Linux and Windows job titles on GitHub (llvm#142101)

Buildkite has a bunch of custom emoji that include Linux and Windows
logos -
https://github.com/buildkite/emojis?tab=readme-ov-file#smileys--emotion.

GitHub doesn't have these so let's just use a penguin and a generic
window. 🐧 🪟

These are standard emoji so Buildkite does support them too, but there's
no motivation to change it there.

Plus, I think the metrics collection might be tied to Buildkite pipeline
name so keeping it the same saves hassle there.

Author: DavidSpickett

.ci/monolithic-linux.sh

@@ -47,7 +47,7 @@ function at-exit {
     python3 "${MONOREPO_ROOT}"/.ci/generate_test_report_buildkite.py ":linux: Linux x64 Test Results" \
       "linux-x64-test-results" $retcode "${BUILD_DIR}"/test-results.*.xml
   else
-    python3 "${MONOREPO_ROOT}"/.ci/generate_test_report_github.py ":linux: Linux x64 Test Results" \
+    python3 "${MONOREPO_ROOT}"/.ci/generate_test_report_github.py ":penguin: Linux x64 Test Results" \
       $retcode "${BUILD_DIR}"/test-results.*.xml >> $GITHUB_STEP_SUMMARY
   fi
 }

.ci/monolithic-windows.sh

@@ -42,7 +42,7 @@ function at-exit {
     python "${MONOREPO_ROOT}"/.ci/generate_test_report_buildkite.py ":windows: Windows x64 Test Results" \
       "windows-x64-test-results" $retcode "${BUILD_DIR}"/test-results.*.xml
   else
-    python "${MONOREPO_ROOT}"/.ci/generate_test_report_github.py ":windows: Windows x64 Test Results" \
+    python "${MONOREPO_ROOT}"/.ci/generate_test_report_github.py ":window: Windows x64 Test Results" \
       $retcode "${BUILD_DIR}"/test-results.*.xml >> $GITHUB_STEP_SUMMARY
   fi
 }