Use SIGTERM instead of SIGINT to kill test child processes (#4015)

Since SIGINT fails to actually kill them on some platforms under some circumstances,
leading to a whole lot of watch tests sitting around for 40 seconds until they
time out.

See derail in the discussion for issue #3989

test/cli/index.js

@@ -124,10 +124,10 @@ runTestSuiteWithSamples(
 					if (config.abortOnStderr) {
 						try {
 							if (await config.abortOnStderr(data)) {
-								childProcess.kill('SIGINT');
+								childProcess.kill('SIGTERM');
 							}
 						} catch (err) {
-							childProcess.kill('SIGINT');
+							childProcess.kill('SIGTERM');
 							done(err);
 						}
 					}