x/tools/gopls: CodeAction: an error in one CodeAction provider should not block another

[adonovan]

See CL 640395 (https://go-review.googlesource.com/c/tools/+/640395/comment/2b081fe5_fb1b18c3/) for context.

[gopherbot]

Change https://go.dev/cl/667115 mentions this issue: gopls/internal/golang: CodeAction: don't fail because of 1 producer