testsuite: g++.dg: rename pr66655 test

The test was being ignored because dg.exp looks for .C in g++.dg/.

gcc/testsuite/ChangeLog:
	PR target/66655

	* g++.dg/pr66655_1.cc: Move to...
	* g++.dg/pr66655_1.C: ...here.

diff --git a/gcc/testsuite/g++.dg/pr66655_1.cc b/gcc/testsuite/g++.dg/pr66655_1.C
similarity index 100%
rename from gcc/testsuite/g++.dg/pr66655_1.cc
rename to gcc/testsuite/g++.dg/pr66655_1.C