Fix LIBPATCH for mongodb_tls.py (#174)

Otherwise charming-actions/release-libraries cannot publish it:

> /snap/bin/charmcraft publish-lib charms.mongodb.v0.mongodb_tls
> ...
> mongodb_tls will be updated from 0.3 to 0.5
> ...
> Library charms.mongodb.v0.mongodb_tls has a wrong LIBPATCH number,
> it's too high and needs to be consecutive, Charmhub highest version is
0.3.

lib/charms/mongodb/v0/mongodb_tls.py

@@ -32,7 +32,7 @@
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 5
+LIBPATCH = 4
 
 
 logger = logging.getLogger(__name__)