[Github] Rename llvm-tests.yml workflow (llvm#153866)

This check used to also run tests for everything, but has since been
modified to only run the ABI tests with actual testing being run through
the premerge configuration. This patch renames the workflow to better
reflect this.

Author: boomanaiden154

.github/workflows/llvm-tests.yml renamed to .github/workflows/llvm-abi-tests.yml

@@ -1,4 +1,4 @@
-name: LLVM Tests
+name: LLVM ABI Tests
 
 permissions:
   contents: read