libstdc++: Fix failing filesystem::path tests (PR 93244)

libstdc++: Fix failing filesystem::path tests (PR 93244)

The checks for PR 93244 don't actually pass on Windows (which is the
target where the bug is present) because of a different bug, PR 94063.

This adjusts the tests to not be affected by 94063 so that they verify
that 93244 was fixed.

	PR libstdc++/93244
	* testsuite/27_io/filesystem/path/generic/generic_string.cc: Adjust
	test to not fail due to PR 94063.
	* testsuite/27_io/filesystem/path/generic/utf.cc: Likewise.
	* testsuite/27_io/filesystem/path/generic/wchar_t.cc: Likewise.