Show full diffs on CI

So when gix-packetline-blocking/src was not updated, the diff from
running the script is shown in full.

Right now this is to investigate how the script does not seem to
work on macOS, but it may be useful to keep it.

.github/workflows/ci.yml

@@ -205,8 +205,14 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - name: Check that working tree is initially clean
-        run: git status; set -x; git diff --quiet
+        run: |
+          set -x
+          git status
+          git diff --exit-code
       - name: Regenerate gix-packetline-blocking/src
         run: etc/copy-packetline.sh
       - name: Check that gix-packetline-blocking/src was already up to date
-        run: git status; set -x; git diff --quiet
+        run: |
+          set -x
+          git status
+          git diff --exit-code