ubuntu-latest support

Tracking item for **ubuntu-latest** queue support.

As of the beta release, the Microsoft Security Code Analysis (MSCA) CLI that powers this action has difficulties running on unix systems do to pathing issues of case sensitivity and backslashes.

The work to fix those components within the MSCA CLI is in progress with an ETA of end of July.

Once pushed to nuget.org, the action will automatically pick up the new version of the MSCA CLI, fixing the **ubuntu-latest** workflow and badge on the main README page, when rerun.

The **Limitations** portion will be updated to remove this limitation.

No source files or tests are named. First check whether the MSCA CLI fix has been published to nuget.org, then rerun the ubuntu-latest workflow and verify its badge; done includes removing the corresponding limitation from the main README.

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