[GitHub] Update repo lockdown to exclude lldb

This change enables the LLDB project to begin experimenting with
pull-request workflows to help identify issues was we move toward
adopting pull requests.

Reviewed By: tstellar, JDevlieghere

Differential Revision: https://reviews.llvm.org/D155315

.github/workflows/repo-lockdown.yml

@@ -7,6 +7,7 @@ on:
       - 'libcxxabi/**'
       - 'libunwind/**'
       - 'runtimes/**'
+      - 'lldb/**'
 
 permissions:
   pull-requests: write