At some point we need to rebuild CI containers with Composer 2.0 bundled, rather than Composer 1.x
In https://gerrit.wikimedia.org/r/c/mediawiki/vendor/+/667051/2/composer.json I changed the `composer-plugin-api` version to `^2.0` to prevent (after it's merged) anyone accidentally running things with composer 1.x, but it won't pass CI.
Certainly, for now, it could be `^1.1||^2.0`, but eventually, it seems a useful safeguard to have
MediaWiki 1.31 doesn't support composer 2, and never will... And is EOL in June 2021, so we probably don't care.
At some point, https://blog.packagist.com/deprecating-composer-1-support/ will start to affect us
>Reduced v1 metadata API update rate starting in May 2021
>The update rate for new versions will be reduced from every-minute currently to once every 15 minutes. This means new releases will take a few minutes longer to be available for installation with Composer 1.x.
I know 15 minutes isn't a lot, but it's going to be enough in cases for CI's composer queries to fail for a little while...