cmake.cygclass: Add a src_test which invokes the cmake test driver

See https://cygwin.com/pipermail/cygwin-apps/2023-October/043227.html

> src_test is not redefined in cmake.cygclass (and ninja.cygclass) in cygport-0.36.3. Therefore, I defined src_test in json-c.cygport.
>
> - https://github.com/cygwin/cygport/blob/0.36.6/cygclass/cmake.cygclass
> - https://github.com/cygwin/cygport/blob/0.36.6/cygclass/ninja.cygclass
>
> I agree that it would be preferable to have src_test defined in one of these cygclasses.

The test is executed with or without CYGCMAKE_GENERATOR=Ninja.

cygclass/cmake.cygclass

@@ -215,6 +215,14 @@ src_compile() {
 }
 #****
 
+#****o* cmake.cygclass/src_test (cmake)
+#  DEFINITION
+src_test() {
+	cd ${B}
+	ctest
+}
+#****
+
 #****o* cmake.cygclass/src_install (cmake)
 #  DEFINITION
 src_install() {