Fix coverage report path to use PROJECT_DIR instead of COVERAGE_BUILD_DIR

The collect-coverage.sh script outputs lcov.info to qt6-after/qt6-migrated-benchmark/coverage/
not to build-coverage/coverage/. Updated pattern to use ${PROJECT_DIR}/coverage/lcov.info.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Entire-Checkpoint: 0f4ad2ce4fdb

Jenkinsfile

@@ -137,7 +137,7 @@ pipeline {
           }
           post {
             always {
-              recordCoverage tools: [[parser: 'LCOV', pattern: "${COVERAGE_BUILD_DIR}/coverage/lcov.info"]],
+              recordCoverage tools: [[parser: 'LCOV', pattern: "${PROJECT_DIR}/coverage/lcov.info"]],
                              sourceCodeRetention: 'LAST_BUILD'
             }
           }