Update README badges (#3789)
Update README badges (#3789)

* Remove inactive Dependabot badge

https://github.com/dependabot/dependabot-core/issues/1912

* Remove misconfigured CodeFactor badge

Currently only gh-pages branch is being checked by CodeFactor

* Make FOSSA badge report on correct project

It was rendering the badge for detekt's IntelliJ plugin, not the primary
detekt project.

* Show pre-merge CI run status for main branch only
arturbosch/detekt,arturbosch/detekt,arturbosch/detekt