c++: Fix a pasto in the PR120471 fix [PR120940]

No idea how this slipped in, I'm terribly sorry.
Strangely nothing in the testsuite has caught this, so I've added
a new test for that.

2025-07-03  Jakub Jelinek  <jakub@redhat.com>

	PR c++/120940
	* typeck.cc (cp_build_array_ref): Fix a pasto.

	* g++.dg/parse/pr120940.C: New test.
	* g++.dg/warn/Wduplicated-branches9.C: New test.

(cherry picked from commit dc90649466a54ab61926d88500a05f59a55cb055)
3 files changed