GCC pragma fixed.

src/catch2/catch_decomposer.h

@@ -28,7 +28,7 @@
 #  pragma clang diagnostic ignored "-Wsign-compare"
 #elif defined __GNUC__
 #  pragma GCC diagnostic push
-#  pragma clang diagnostic ignored "-Wsign-compare"
+#  pragma GCC diagnostic ignored "-Wsign-compare"
 #endif
 
 namespace Catch {