cmd/go/internal/modfetch: fix retractions slice initial length not zero

When make slice of retractions, it should have initial length zero, to append more VersionIntervals.

Currently without the zero length, the capacity used will be doubled after the appending, looks like a bug.

Change-Id: Id3acaeffe557ca1d15c864b0377a66fee3a41f6c
GitHub-Last-Rev: ed5fd5f
GitHub-Pull-Request: #60354
Reviewed-on: https://go-review.googlesource.com/c/go/+/497118
Auto-Submit: Bryan Mills <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: futurist

src/cmd/go/internal/modfetch/coderepo.go

@@ -1013,7 +1013,7 @@ func (r *codeRepo) retractedVersions(ctx context.Context) (func(string) bool, er
 	if err != nil {
 		return nil, err
 	}
-	retractions := make([]modfile.VersionInterval, len(f.Retract))
+	retractions := make([]modfile.VersionInterval, 0, len(f.Retract))
 	for _, r := range f.Retract {
 		retractions = append(retractions, r.VersionInterval)
 	}