Update validation for github owner to allow _

[shahzad31]

Update validation for github owner to allow _ !!

follow up to https://github.com/elastic/elastic-package/pull/1564

[jsoriano]

Oh, and looking to the failures in CI you will need to update the pattern that appears in error messages in tests.

[elasticmachine]

:green_heart: Build Succeeded

• Buildkite Build
• Commit: d1e47cc881365c12ed0a711a8295a66968623ab8

History

• :green_heart: Build #417 succeeded 65a4487d53fc1298cfa2180a7d4f9f4599128d48
• :broken_heart: Build #413 failed 1a9253532f51ce58a265f8370526f19b4e66410e