ci: coverity: Update Variable Rules for Coverity Scan Job

Enhanced variable rules to ensure the Coverity scan job runs for:
1. Every new tag.
2. Scheduled pipelines on protected branches, configured for nightly runs.
3. require a scoped label ci::allow-expensive-jobs activation for scans on merge requesrs targeting protected branches to ensure compliance.

References: PCF-1795

Signed-off-by: Mouna Aloui <mouna.aloui@softathome.com>

.gitlab/coverity.yml

@@ -16,13 +16,17 @@ include:
     BRIDGE_COVERITY_CONNECT_USER_PASSWORD: $COVERITY_PASSPHRASE
     BRIDGE_GITLAB_USER_TOKEN: $GITLAB_API_KEY_EXTERNAL
     BRIDGE_COVERITY_LOCAL: true
+    BRIDGE_BREAK: false
     BRIDGE_COVERITY_CLEAN_COMMAND: make clean
     # INCLUDE_DIAGNOSTICS: 'true'
   rules:
-    - if: ($CI_COMMIT_REF_NAME =~ $SCAN_BRANCHES && $CI_PIPELINE_SOURCE != 'merge_request_event')
+    - if: $CI_COMMIT_REF_PROTECTED && $CI_COMMIT_TAG
       variables:
         BRIDGE_COVERITY_CONNECT_POLICY_VIEW: Outstanding Issues
-    - if: ($CI_MERGE_REQUEST_TARGET_BRANCH_NAME =~ $SCAN_BRANCHES && $CI_PIPELINE_SOURCE == 'merge_request_event')
+    - if: $CI_PIPELINE_SOURCE == "schedule"
+      variables:
+        BRIDGE_COVERITY_CONNECT_POLICY_VIEW: Outstanding Issues
+    - if: '$CI_MERGE_REQUEST_TARGET_BRANCH_PROTECTED == "true" && $CI_MERGE_REQUEST_LABELS =~ /ci::allow-expensive-jobs/'
   before_script:
     - export BRIDGE_COVERITY_BUILD_COMMAND="make -j $(nproc)"
     - apt-get -qq update && apt-get install -y curl file unzip