Disable CI build with Oracle and Vert.x snapshot

There's something wrong with it and it's causing a lot of failures
(sending a huge amount of e-mails).

Because it seems a problem with the Vert.x driver,
I'm going to disable it for now and re-enable it as soon as we have
a fix.

Author: DavideD

.github/workflows/tracking-vertx-4.build.yml

@@ -87,7 +87,7 @@ jobs:
     strategy:
       matrix:
         vertx-version: [ '[4.2,4.3)' ]
-        db: [ 'MariaDB', 'MySQL', 'PostgreSQL', 'DB2', 'CockroachDB', 'MSSQLServer', 'Oracle' ]
+        db: [ 'MariaDB', 'MySQL', 'PostgreSQL', 'DB2', 'CockroachDB', 'MSSQLServer' ]
     steps:
       - uses: actions/checkout@v2
       - name: Set up JDK 11