t0301: actually test credential-cache on Windows

Commit 2406bf5 (Win32: detect unix socket support at runtime,
2024-04-03) introduced a runtime detection for whether the operating
system supports unix sockets for Windows, but a mistake snuck into the
tests. When building and testing Git without NO_UNIX_SOCKETS we
currently skip t0301-credential-cache on Windows if unix sockets are
supported and run the tests if they aren't.

Flip that logic to actually work the way it was intended.

Signed-off-by: Matthias Aßhauer <[email protected]>
Signed-off-by: Johannes Schindelin <[email protected]>

t/t0301-credential-cache.sh

@@ -12,7 +12,7 @@ test -z "$NO_UNIX_SOCKETS" || {
 if test_have_prereq MINGW
 then
 	service_running=$(sc query afunix | grep "4  RUNNING")
-	test -z "$service_running" || {
+	test -n "$service_running" || {
 		skip_all='skipping credential-cache tests, unix sockets not available'
 		test_done
 	}