fix(terraform): support github repo source url with underscores

[raspy8766]

Changes:

Adds underscore to the list of whitelisted characters for the githubRefMatchRegex so that repositories with an underscore don't get truncated for Terraform and Terragrunt managers.

Context:

Our repo has an underscore and was getting truncated like below which resulted in us getting the "Failed to look up dependency" warning message:

Before

After

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

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

I have verified these changes via:

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

[CLAassistant]

All committers have signed the CLA.

[viceice]

Should have new tests.

[raspy8766]

Should have new tests.

@viceice Added some unit tests for the github source regex

[viceice]

My expectation was to add tests for the function which are suing the regexes and not the regex directly 🤔

@rarkins Should we ok with only testing the regex directly?

[rarkins]

I think that's ok, thanks

[renovate-release]

🎉 This PR is included in version 25.3.1 🎉

The release is available on:

• GitHub release
• 25.3.1

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