Use the channel's dist-tag when counting published prereleases #163

We are publishing to GCP's registry on an alpha channel. Our second channel publish tried to reuse 0.1.0-alpha.0 for every package, and the registry rejected each one with "Requested version(0.1.0-alpha.0) already exists".

bumpy finds the next prerelease number with npm info <name> versions --json. That command doesn't list every version. When the spec has no version, npm looks the package up through its tag config, which defaults to latest. If the package has no latest dist-tag, npm prints nothing and exits 0. You can see this in npm 11's lib/commands/view.js, which throws "No match found" for any other tag but returns quietly for latest. bumpy then fails on JSON.parse(""), the catch returns [], and the counter starts over at 0.

npmjs.org always sets latest on a package's first publish I'm guessing, so this doesn't show up there. GCP only appears to set the dist-tag you publish with. We ran these on the CI runner after the first alpha publish:

Our workaround is to explicitly set npm_config_tag based on the branch.