[docs] Breaking change detection configuration references outdated RegExp

[seniorquico]

The ignore_unstable_packages section on the Breaking Change Detection configuration page includes outdated PACKAGE_VERSION_SUFFIX references.

v\d+test.*
v\d+(alpha|beta)\d+
v\d+p\d+(alpha|beta)\d+

In response to #420, the trailing number was made optional. It's correctly documented in the PACKAGE_VERSION_SUFFIX reference.

It's a little thing, but it'd be great if the docs could be updated to reflect the latest behavior. I didn't think I needed to click through, and we made some unnecessary decisions as a result.

[amckinney]

Thanks for the report, this is updated now!