chore: update gcr and docker cred helpers (#2910)

vendor/github.com/sourcegraph/conc/internal/multierror/multierror_go119.go

@@ -0,0 +1,10 @@
+//go:build !go1.20
+// +build !go1.20
+
+package multierror
+
+import "go.uber.org/multierr"
+
+var (
+	Join = multierr.Combine
+)

vendor/github.com/sourcegraph/conc/internal/multierror/multierror_go120.go

@@ -0,0 +1,10 @@
+//go:build go1.20
+// +build go1.20
+
+package multierror
+
+import "errors"
+
+var (
+	Join = errors.Join
+)