Enable unit test artifacts for gcov jobs

Without using the build artifacts from the unit test jobs in the
bookworm tests, the gcov would be incomplete.

(cherry picked from commit e5636598a5)

.gitlab-ci.yml

@@ -53,6 +53,9 @@ variables:
 
   HYPOTHESIS_PROFILE: "ci"
 
+  # Some jobs may clean up the build artifacts unless this is set to 0.
+  CLEAN_BUILD_ARTIFACTS_ON_SUCCESS: 1
+
 default:
   # Allow all running CI jobs to be automatically canceled when a new
   # version of a branch is pushed.
@@ -364,7 +367,7 @@ stages:
     - >
       "$PYTEST" --junit-xml="$CI_PROJECT_DIR"/junit.xml -n "$TEST_PARALLEL_JOBS" | tee pytest.out.txt
     - '( ! grep -F "grep: warning:" pytest.out.txt )'
-    - make clean >/dev/null 2>&1
+    - test "$CLEAN_BUILD_ARTIFACTS_ON_SUCCESS" -eq 0 || ( cd ../../.. && make clean >/dev/null 2>&1 )
   after_script:
     - test -n "${OUT_OF_TREE_WORKSPACE}" && cd "${OUT_OF_TREE_WORKSPACE}"
     - *display_pytest_failures
@@ -434,7 +437,7 @@ stages:
     - test -n "${OUT_OF_TREE_WORKSPACE}" && cd "${OUT_OF_TREE_WORKSPACE}"
   script:
     - make -j${TEST_PARALLEL_JOBS:-1} -k unit V=1
-    - make clean >/dev/null 2>&1
+    - test "$CLEAN_BUILD_ARTIFACTS_ON_SUCCESS" -eq 0 || make clean >/dev/null 2>&1
   after_script:
     - test -d bind-* && cd bind-*
     - REALSOURCEDIR="$PWD"
@@ -888,7 +891,8 @@ system:gcc:bookworm:amd64:
   <<: *system_test_gcov_job
   variables:
     CI_ENABLE_ALL_TESTS: 1
-  needs:
+    CLEAN_BUILD_ARTIFACTS_ON_SUCCESS: 0
+  needs:  # using artifacts from unit test job is required for gcov
     - job: unit:gcc:bookworm:amd64
       artifacts: true
 
@@ -897,6 +901,7 @@ unit:gcc:bookworm:amd64:
   <<: *unit_test_gcov_job
   variables:
     CI_ENABLE_ALL_TESTS: 1
+    CLEAN_BUILD_ARTIFACTS_ON_SUCCESS: 0
   needs:
     - job: gcc:bookworm:amd64
       artifacts: true