Dependency update and AddonsUpdater fixes

[chillu]

The environments are already on 7.3, but due to the composer constraint, the core modules didn't update to newer versions (framework was stuck on 4.4). Doing this because of some strange behaviour where QueuedJobDescriptor records have started filling up the database with garbage messages like this:

a:601:{i:0;s:28:"[2020-11-16 22:33:25][INFO] ";i:1;s:120:"[2020-11-17 03:27:46][INFO] dylangrech92/seotoolbox 298 Could not parse version constraint ^: Invalid version string "^"";i:

It's unclear where this came from, since we didn't change the production deploys for months. Could be changes to packagist API responses.

See https://github.com/silverstripe/addons.silverstripe.org/issues/257

Context: https://silverstripeltd.slack.com/archives/CLXKD9X51/p1605554600486700

[chillu]

Found more bugs, essentially the build throttling on our side didn't work.

What should happen:

• Every 6 hours, ~3k API calls to Packagist API retrieve all versions through AddonUpdater
• For each addon that has new versions and hence require a build (usually very few), trigger a job for AddonBuilder
• AddonBuilder runs the same Packagist API call for this addon only

What did happen:

• Every 6 hours, ~3k API calls to Packagist API retrieve all versions through AddonUpdater
• Every addon triggered a job with AddonBuilder, which lead to another ~3k API calls

So while jobs seem to be limited to single concurrency, that still amounts to a craptonne of API calls, which likely resulted in rate limiting observed in https://github.com/silverstripe/addons.silverstripe.org/issues/257. I've fixed the bugs leading to this behaviour, and reduced the update frequency from 6 to 12 hours. So over a day, that'll reduce the API calls from 36k to around 6k.