[DebugInfo] Prevent inlining in NRVO-string test cases

Since the new pass manager has been enabled by default these tests had their
-O1 variations failing due to the tested functions being inlined. This just
adds no_inline to the respective code similar to what we did in other
tests (e.g. aa56b30014d96700b2fc945be11866789f341d38 ).

GitOrigin-RevId: a874d182c61c7f8e5291c718b40be0e133bf21f0