feat(circleci): target all YAML files in .circleci directory

[mkniewallner]

Changes

Update the default fileMatch regex in CircleCI manager to target all YAML files under .circleci directory.

Note that there were no tests on this, and it looks like most other managers do not have ones. I took the liberty to add some but if you feel like this is overkill, I can remove them.

Context

Discussed in #27807. Per https://circleci.com/docs/using-dynamic-configuration/, CircleCI supports dynamic configuration to spread configuration across multiple files, where each of them could contain dependencies (e.g. orbs).

Documentation (please check one with an [x])

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• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[renovate-release]

🎉 This PR is included in version 37.233.0 🎉

The release is available on:

• GitHub release
• npm package (@latest dist-tag)
• 37.233.0

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