x/tools/gopls: add dependency suggested fix broken with experimentalWorkspaceModule

[stamblerre]

Similar to the go mod tidy and update go.sum quick fixes, the add dependency quick fix does not work in experimental workspace module mode. The issue is again that we don't associate the fix with the correct module, which can lead to unpredictable results.

[gopherbot]

Change https://golang.org/cl/291192 mentions this issue: internal/lsp: refactor go command error handling