ci: make one of the clang jobs use MESON_RSP_THRESHOLD=0

Ensure that any changes to clang or errors in meson's rspfile implementation
are caught, since this has just happened for GCC 16.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

.github/workflows/os_comp.yml

@@ -98,7 +98,8 @@ jobs:
             RUN_TESTS_ARGS: '--no-unittests'
             CC: 'gcc'
             CXX: 'g++'
-          - CC: 'clang'
+          - MESON_RSP_THRESHOLD: '0'
+            CC: 'clang'
             CXX: 'clang++'
           - MESON_ARGS: '--unity=on'
             RUN_TESTS_ARGS: '--no-unittests'