do not queue jobs for readOnly wikis

[deer-wmde]

• a suggestion to skip mw job enqueueing if wikis are set to readOnly
• currently it seems unclear if MW jobs already skip readOnly wikis

related to https://phabricator.wikimedia.org/T412202

[deer-wmde]

I did some digging into https://github.com/wbstack/mediawiki code and glanced over search results of ->push( $job (mind the whitespace) - and it may be fiiine ? i.e. most jobs seem to get scheduled after actions that aren't possible during read-only mode

[outdooracorn]

Thanks for looking into this, Dena!

Closing as per decision in https://phabricator.wikimedia.org/T412195#11507411

I'm tempted to leave it for now, given that:

• we no longer have any mediawiki-139 pods
• this type of error will likely only happen again if a future update removes tables that are read by the API and while the Wikis are being updated
• it doesn't cause any issues, just some extra log spam

Can reopen, in the future, if needed.