Run URL conventions Danger only on added lines

[PyvesB]

Follow up to #11478. I noticed in #11536 that the warnings are emitted even if deleting an existing badge that does not follow URL conventions. This PR adds a ^\+[...]m bit to the regex to only look for added lines, i.e. ones starting with +. I also combined the two regexes into one.

I've tested this with the following command which no longer produces the false positive:

DANGER_GITHUB_API_TOKEN=<token> npm run danger -- pr https://github.com/badges/shields/pull/11536

Danger: ✓ passed, found only messages.
## Messages
:sparkles: Thanks for your contribution to Shields, @PyvesB!

Other cases still trigger as expected:

DANGER_GITHUB_API_TOKEN=<token> npm run danger -- pr https://github.com/badges/shields/pull/11489

Danger: ✓ found only warnings, not failing the build
## Warnings
This PR modified service code. <br>Please run tests by [including affected services in the pull request title](https://github.com/badges/shields/blob/master/CONTRIBUTING.md#running-service-tests-in-pull-requests).
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Found badge URL that may not follow our standard route abbreviations in `services/comfyui/comfyui-downloads.service.js`. <br>Please ensure you've reviewed our [conventions](https://github.com/badges/shields/blob/master/doc/badge-urls.md).
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Found badge URL that may not follow our standard route abbreviations in `services/comfyui/comfyui-version.service.js`. <br>Please ensure you've reviewed our [conventions](https://github.com/badges/shields/blob/master/doc/badge-urls.md).
## Messages
:sparkles: Thanks for your contribution to Shields, @neverbiasu!
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Thanks for contributing to our documentation. We :heart: our [documentarians](http://www.writethedocs.org/)!

[github-actions]

	Messages
📖	✨ Thanks for your contribution to Shields, @PyvesB!

Generated by 🚫 dangerJS against b62da50