docs: update description for why credentials are committed

Author: rhblind

.mosquitto/README.md

@@ -1,3 +1,3 @@
 The files in this directory is part of the test suite and are *not* commited by accident.
-They are valid credentials for both [test.mosquitto.org](https://test.mosquitto.org/), the public
-Mosquitto test server and the local docker container used to test and develop this library.
+They are valid credentials for the docker container used for local testing and development, 
+and are also used by the GitHub Actions workflow test suite.