ci: retrigger PRB - now with inlined cache logic (no external helper)

Previous PRB run failed because the Jenkinsfile referenced
${WORKSPACE}/jenkins-scripts/stable/PRB/prb-cached-test.sh, but the
setup stage's cleanWs() wipes the testing-repo checkout before
stashing only wolfProvider/, so the helper wasn't on the parallel
agents. testing PR #958 b89d0b49 inlines the cache logic directly
into the test-wp-cs sh block.

Author: aidangarske