coroutines, testsuite: Rename a test, NFC.

The test was committed with a placeholder name, this
renames it as described in the PR.

gcc/testsuite/ChangeLog:

	* g++.dg/coroutines/pr9xxxx-mismatched-traits-and-promise-prev.C: Moved to...
	* g++.dg/coroutines/pr94760-mismatched-traits-and-promise-prev.C: ...here.

diff --git a/gcc/testsuite/g++.dg/coroutines/pr9xxxx-mismatched-traits-and-promise-prev.C b/gcc/testsuite/g++.dg/coroutines/pr94760-mismatched-traits-and-promise-prev.C
similarity index 100%
rename from gcc/testsuite/g++.dg/coroutines/pr9xxxx-mismatched-traits-and-promise-prev.C
rename to gcc/testsuite/g++.dg/coroutines/pr94760-mismatched-traits-and-promise-prev.C