internal/lsp/source: don't mark fillreturns as high confidence

It's not ready for the release yet (see golang/go#38707).

Change-Id: I04c1d8ec4ed815efb3e4c2d3c88cba3ec164755e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/233527
Run-TryBot: Rebecca Stambler <[email protected]>
Reviewed-by: Heschi Kreinick <[email protected]>

Author: stamblerre

internal/lsp/source/options.go

@@ -584,7 +584,7 @@ func typeErrorAnalyzers() map[string]Analyzer {
 			Analyzer:       fillreturns.Analyzer,
 			enabled:        true,
 			FixesError:     fillreturns.FixesError,
-			HighConfidence: true,
+			HighConfidence: false,
 		},
 		nonewvars.Analyzer.Name: {
 			Analyzer:   nonewvars.Analyzer,