DO NOT COMMIT: tweak premerge to use custom image

For help in testing the prior commit

Author: gburgessiv

.github/workflows/premerge.yaml

@@ -35,6 +35,8 @@ jobs:
         github.repository_owner == 'llvm' &&
         (github.event_name != 'pull_request' || github.event.action != 'closed')
     runs-on: llvm-premerge-linux-runners
+    container:
+        image: ghcr.io/gburgessiv/llvm-ci-with-checkout:latest
     steps:
       - name: Checkout LLVM
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
@@ -52,6 +54,8 @@ jobs:
         # are ready for people to start recieving notifications.
         continue-on-error: true
         run: |
+          ls /home/gha
+          exit 1
           git config --global --add safe.directory '*'
 
           modified_files=$(git diff --name-only HEAD~1...HEAD)
@@ -110,6 +114,7 @@ jobs:
       - name: Compute Projects
         id: vars
         run: |
+          exit 1
           modified_files=$(git diff --name-only HEAD~1...HEAD)
           modified_dirs=$(echo "$modified_files" | cut -d'/' -f1 | sort | uniq)
 
@@ -170,6 +175,7 @@ jobs:
         uses: llvm/actions/install-ninja@main
       - name: Build and Test
         run: |
+          exit 1
           modified_files=$(git diff --name-only HEAD~1...HEAD)
           modified_dirs=$(echo "$modified_files" | cut -d'/' -f1 | sort -u)