add h2 to the readme and fix the dialects package

[fwbrasil]

Problem

We forgot to add h2 to the readme when we introduced the new dialect.

Solution

Add it!

Notes

I've also fixed the dialects package.

Checklist

• Unit test all changes
• Update README.md if applicable
• Add [WIP] to the pull request title if it's work in progress
• Squash commits that aren't meaningful changes
• Run sbt scalariformFormat test:scalariformFormat to make sure that the source files are formatted

@getquill/maintainers