Update module golang.org/x/sync to v0.7.0

This MR contains the following updates:

Package	Type	Update	Change
golang.org/x/sync	require	minor	v0.3.0 -> v0.7.0

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vendor/golang.org/x/sync/singleflight/singleflight.go

@@ -31,6 +31,15 @@ func (p *panicError) Error() string {
 	return fmt.Sprintf("%v\n\n%s", p.value, p.stack)
 }
 
+func (p *panicError) Unwrap() error {
+	err, ok := p.value.(error)
+	if !ok {
+		return nil
+	}
+
+	return err
+}
+
 func newPanicError(v interface{}) error {
 	stack := debug.Stack()