internal/lsp/analysis: update fillreturns title
internal/lsp/analysis: update fillreturns title

Update the title of the diagnostic to account for the fact that
fillreturns can also use in-scope variables to fill in values.

Change-Id: Ib506af76a4187ef611e96b2602f301432fcbccf0
Reviewed-on: https://go-review.googlesource.com/c/tools/+/253278
Run-TryBot: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools