Update cats-core to 2.6.1

[scala-steward]

Updates org.typelevel:cats-core from 2.3.1 to 2.6.1.
GitHub Release Notes - Changelog - Version Diff

I'll automatically update this PR to resolve conflicts as long as you don't change it yourself.

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Files still referring to the old version number

The following files still refer to the old version number (2.3.1).
You might want to review and update them manually.

modules/provider-oauth2/src/main/scala/silhouette/provider/oauth2/OAuth2Provider.scala
modules/provider-oauth2/src/test/scala/silhouette/provider/oauth2/OAuth2ProviderSpec.scala

Ignore future updates

Add this to your .scala-steward.conf file to ignore future updates of this dependency:

updates.ignore = [ { groupId = "org.typelevel", artifactId = "cats-core" } ]

labels: library-update, semver-minor, old-version-remains