ci: clean up workflow files

[innocenzi]

This pull request cleans up workflow files:

• I made the task names consistent in casing
• I removed two seemingly unused workflows
• I fixed coding-conventions.yml, which was corrupted in a rebase
• I removed the updating of CHANGELOG.md in the GitHub release workflow, as that doesn't work with branch protections
• I took the opportunity to update package.json scripts

[aidan-casey]

@innocenzi looks like there are still a few cases of the brand names being off (another phpstan, etc.). Once that's cleaned up, I like it and let's get this merged.

Side note, this is one of those things we should probably document in contributing.

[innocenzi]

@aidan-casey Thanks! Here I was, thinking I was clever with my perfectionism, and I missed one 😔