Report Docker disk usage per stage in the helper-rust coverage job

The Docker host's storage in this job is ~20G, and the container filesystem
measurement added in the previous commit shows it is already 18G/93% full when
the test phase starts, then hits 100% partway through, which is what breaks
RaspSqliTests. That baseline is established before any test runs, so it comes
from the cache load and the coverage-instrumented Rust build rather than from
the tests. Report `docker system df` at each stage to attribute it.

Author: cataphract

.gitlab/generate-appsec.php

@@ -291,10 +291,23 @@
         TERM=dumb ./gradlew loadCaches --info
       fi
 
+      # The Docker host's storage is only ~20G here, and this job has been
+      # running it out during the tests, which surfaces as unrelated containers
+      # failing (a full disk leaves MySQL unable to write, so queries are never
+      # answered and clients hang). Report what occupies it at each stage.
+      report_docker_disk() {
+        echo "===== docker disk usage: $1 ====="
+        docker system df || true
+        docker system df -v 2>/dev/null | sed -n '/VOLUME NAME/,$p' | head -30 || true
+      }
+      report_docker_disk 'after loadCaches'
+
       TERM=dumb ./gradlew buildPortableLibdatadogPhp \
         --info -Pbuildscan --scan -PuseHelperRustCoverage
+      report_docker_disk 'after buildPortableLibdatadogPhp'
       TERM=dumb ./gradlew test8.3-release-ssi test8.4-release-zts-ssi \
         --info -Pbuildscan --scan -PcheckCoreDumps -PuseHelperRustCoverage
+      report_docker_disk 'after tests'
       TERM=dumb ./gradlew saveCaches --info
     - |
       cd "$CI_PROJECT_DIR"