gopls: update to 0.15.2

This release fixes the following regressions in gopls@v0.15.0+.

- a crash when encountering a test file excluded via build tags, which also
  contained an invalid import of a main package. This could occur in a
  tools_test.go file implementing the common pattern for tool dependencies.
- spurious import errors in multi-root workspaces. In some scenarios, the new
  zero-config logic added in gopls@v0.15.0 resulted in inaccurate errors about
  missing imports. This could occur when module A has a local replace of module
  B, and A and B are open as a separate workspace folders.
- a crash when working on modules with a go directive of the form go a.b.c,
  when gopls was compiled with Go 1.20 or earlier.
- a crash when SignatureHelp is cancelled (found via telemetry)
- a crash in references when one of the package files is missing a package
  declaration (found via telemetry)

These last two crashes are worth highlighting. Both were found via the (off by
default) automated crash reporting added in gopls@v0.15.0. Both were unlikely
to get reported via GitHub issues, because they won't happen frequently enough
for most LSP clients to notify the user. This is a perfect example of how
telemetry can help us deliver a more reliable product than would be possible
without automated reporting.

(bsiegert)