ci(coverity): output the build log upon error

It is quite helpful to know what Coverity said, exactly, in case it
fails to analyze the code.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.github/workflows/coverity.yml

@@ -149,7 +149,11 @@ jobs:
         run: |
           export PATH="$PATH:$RUNNER_TEMP/cov-analysis/bin" &&
           cov-configure --gcc &&
-          cov-build --dir cov-int make
+          if ! cov-build --dir cov-int make
+          then
+            cat cov-int/build-log.txt
+            exit 1
+          fi
       - name: package the build
         run: tar -czvf cov-int.tgz cov-int
       - name: submit the build to Coverity Scan