MDL-83470 environment: Put back Oracle support for now

Even though Oracle support is planned to be dropped for 5.0, the
actual issue that drops it (MDL-83172) has not yet landed. So, it's
better to keep this in environment.xml for now and defer its removal
from environment.xml in MDL-83172.

admin/environment.xml

@@ -4714,6 +4714,7 @@
       <VENDOR name="mysql" version="8.4" />
       <VENDOR name="postgres" version="14" />
       <VENDOR name="mssql" version="14.0" />
+      <VENDOR name="oracle" version="19" />
     </DATABASE>
     <PHP version="8.2.0" level="required">
     </PHP>