build: add CodeQL config

[tomlongridge]

Goal

Adds CodeQL scanning, but only for Ruby test code as Objective-C is currently not supported.

[github-actions[bot]]

	1 Error
:no_entry_sign:	Only release PRs should target the master branch

Bugsnag.framework binary size did not change - 713,264 bytes

    FILE SIZE        VM SIZE    
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  [ = ]       0  [ = ]       0    TOTAL

Generated by :no_entry_sign: Danger

[github-advanced-security[bot]]

This pull request sets up GitHub code scanning for this repository. Once the scans have completed and the checks have passed, the analysis results for this pull request branch will appear on this overview. Once you merge this pull request, the 'Security' tab will show more code scanning analysis results (for example, for the default branch). Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results. For more information about GitHub code scanning, check out the documentation.