libc++-infa: Hotfix runner group

The runners-32 group is broken, for reasons...
The easiest fix is to move the jobs to runners-8.
(which needs to be renamed, because they're all actually 30 core
machines)

Author: EricWF

.github/workflows/libcxx-build-and-test.yaml

@@ -185,7 +185,7 @@ jobs:
           std_modules: 'OFF'
         # Use a larger machine for MSAN to avoid timeout and memory allocation issues.
         - config: 'generic-msan'
-          machine: libcxx-runners-32-set
+          machine: libcxx-runners-8-set
           std_modules: 'OFF'
     runs-on: ${{ matrix.machine }}
     steps: