ci: switch x86_64-gnu-debug to use a large disk runner

Full stage 2 build + run-make with full debug info seems to overwhelm
the standard 4c runner's storage capacity.

Author: jieyouxu

Diff for: src/ci/github-actions/jobs.yml

@@ -253,7 +253,9 @@ auto:
     <<: *job-linux-4c
 
   - image: x86_64-gnu-debug
-    <<: *job-linux-4c
+    # This seems to be needed because a full stage 2 build + run-make tests
+    # overwhelms the storage capacity of the standard 4c runner.
+    <<: *job-linux-4c-largedisk
 
   - image: x86_64-gnu-distcheck
     <<: *job-linux-8c