CI (Buildkite): on the platform_linux jobs, after building Julia, make sure that the working directory is clean (#41796)

(cherry picked from commit cb30aa7)

Author: DilumAluthge

.buildkite/pipelines/main/platforms/linux64.yml

@@ -35,6 +35,9 @@ steps:
       make release
       make install
 
+      echo "--- Make sure that the working directory is clean"
+      if [ -z "$(git status --short)" ]; then echo "INFO: The working directory is clean."; else echo "ERROR: The working directory is dirty."; echo "Output of git status:"; git status; exit 1; fi
+
       echo "--- Print Julia version info"
       ./julia -e 'using InteractiveUtils; InteractiveUtils.versioninfo()'