bintray: warn on upload error on uploads

[jonchang]

Previously this would only warn on errors for certain Bintray API requests like publishing. This should now also warn on error for curl POST uploads (if the appropriate flag has been passed).

cc @fxcoudert @dawidd6

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[MikeMcQuaid]

Looks right to me. Will make --warn-on-error considerably more permissive but that seems to be the point.

[jonchang]

There's some kind of issue with the GitHub runners and testing. They would frequently fail with rubygems errors. It took probably 2-3 retries and several force pushes to get this merged.

[MikeMcQuaid]

There's some kind of issue with the GitHub runners and testing. They would frequently fail with rubygems errors. It took probably 2-3 retries and several force pushes to get this merged.

@jonchang what errors and what platform? Do you have any logs you can link to and I can take a look?