ci: Add upterm debugging for C9S build hang

Temporarily limit CI matrix to only run centos-9 job to debug
the build-integration hang that has been occurring for 40+ minutes.
Added upterm action before the build step to allow interactive SSH
debugging of the issue.

This will enable us to investigate why the bcvk disk image build
is hanging specifically on C9S while other distros pass.

Assisted-by: Claude Code (Sonnet 4.5)

.github/workflows/ci.yml

@@ -125,7 +125,9 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        test_os: [fedora-42, fedora-43, centos-9, centos-10]
+        # TEMPORARILY TESTING ONLY C9S FOR DEBUGGING
+        test_os: [centos-9]
+        # test_os: [fedora-42, fedora-43, centos-9, centos-10]
 
     runs-on: ubuntu-24.04
 
@@ -136,6 +138,13 @@ jobs:
         with:
           libvirt: true
 
+      - name: Setup upterm session for debugging
+        uses: owenthereal/action-upterm@v3
+        with:
+          limit-access-to-actor: false
+          limit-access-to-users: cgwalters
+          wait-timeout-minutes: 60
+
       - name: Build container and disk image
         run: |
           tests/build.sh ${{ matrix.test_os }}
@@ -157,7 +166,9 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        test_os: [fedora-42, fedora-43, centos-9, centos-10]
+        # TEMPORARILY TESTING ONLY C9S FOR DEBUGGING
+        test_os: [centos-9]
+        # test_os: [fedora-42, fedora-43, centos-9, centos-10]
 
     runs-on: ubuntu-24.04