Add second CodeQL job to validation pipeline for Go mirror

[dagood]

• Fixes https://github.com/microsoft/go-lab/issues/73

This PR changes the validation pipeline to run two jobs: the "outer" one submits a CodeQL database for microsoft-go, and the "inner" one is manually assigned to point at microsoft-go-mirror so that the CodeQL coverage is recognized by tooling.

Test run: https://dev.azure.com/dnceng/internal/_build/results?buildId=2459481&view=results, which uploaded (note the language and repo):

• https://codeql.microsoft.com/job/f95bf6bc-ee0e-405e-a042-e42fdf2b961a
• https://codeql.microsoft.com/job/24a9450d-9e62-4c8d-b256-0728232a733c
• https://codeql.microsoft.com/job/0991cceb-1599-4be1-82c6-9944ddc48b78
• https://codeql.microsoft.com/job/549f7ead-6770-4e60-9ce8-5312c1bed9c3