gopls/v0.12.2

This is an alias for the gopls/v0.12.1 release, and the gopls command reports its version as v0.12.1.
(It was created in the v0.12.1 release process as a defensive measure during an incident that we are investigating.)

Update (findleyr@): the incident in question was a failure to install "gopls@latest" due to a cached 404 in the sumdb. Many LSP clients install gopls@latest, so we cut v0.12.2 as a stopgap measure to ensure that installing gopls@latest continued to work.

Installing gopls@v0.12.1 eventually worked, after ~30m.