Fix class name in Python Tests (#36538)

metricbeat/tests/system/test_lightmodules.py was failing, it seems we
had a custom class with the name starting in 'Test' and that was
confusing pytest. This commit fixes the issue by renaming the class.

metricbeat/tests/system/test_lightmodules.py

@@ -46,15 +46,15 @@ def test_processors(self):
 
 @contextmanager
 def http_test_server():
-    server = http.server.HTTPServer(('localhost', 0), TestHTTPHandler)
+    server = http.server.HTTPServer(('localhost', 0), HTTPHandlerForTest)
     child = threading.Thread(target=server.serve_forever)
     child.start()
     yield server
     server.shutdown()
     child.join()
 
 
-class TestHTTPHandler(http.server.BaseHTTPRequestHandler):
+class HTTPHandlerForTest(http.server.BaseHTTPRequestHandler):
     def do_GET(self):
         self.send_response(200)
         self.send_header("Content-type", "application/json")