CompatHelper: bump compat for Bibliography to 0.3, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the Bibliography package from 0.2.15 to 0.2.15, 0.3.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[goerz]

@Azzaare I'm a little confused about how this PR got created while I'm not seeing a 0.3 release. Do you have any idea what might have caused CompatHelper to want to bump to a version that apparently doesn't exist?

[cgarling]

Commenting as I noticed my Bibliography.jl is being held to v0.2.20 due to compat restrictions originating from DocumenterCitations.jl (not a big deal but was interested in looking into it).

Bibliography.jl has a 0.3 tag on JuliaHub and there is also an entry for 0.3.0 in the relevant Versions.toml on the general registry.

I do not see a call to JuliaRegistrator in the commit that changed the version to 0.3.0, but I believe it's also possible to register a new version with the registry on JuliaHub directly. In any case, TagBot is only activated with

on:
  issue_comment:
    types:
      - created

so it may be the case that TagBot wasn't triggered to create the new tag / release on GitHub.

[goerz]

Closed with #92