[DebugInfo][dexter] Tweak dexter test for merged values

Tweak dexter-tests/memvars/inline-escaping-function.c added in D94761
(b7e516202eb6) by adding a 'param' use after the merge point. The test XFAILS
with and without this change, but without it the test looks very similar to
memvars/unused-merged-value.c. The test now demonstrates the problem more
clearly.

GitOrigin-RevId: d77a57208770470d546194ad81bd01ae5d94df0d