gopls/internal/regtest/misc: skip vendor test on go1.13

To investigate why changing the minimum go version to go1.13
(and updating the sums) isn't a fix would be a waste of time
since our support for 1.13 is about to go away.

Change-Id: I12ee02faf617318da4733e600ef6312c3ee2865e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/454795
Auto-Submit: Alan Donovan <adonovan@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Alan Donovan <adonovan@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>

Author: adonovan

gopls/internal/regtest/misc/definition_test.go

@@ -293,6 +293,7 @@ func TestGoToCrashingDefinition_Issue49223(t *testing.T) {
 // correct metadata even after an external 'go mod vendor' command
 // causes packages to move; see issue #55995.
 func TestVendoringInvalidatesMetadata(t *testing.T) {
+	testenv.NeedsGo1Point(t, 14)
 	const proxy = `
 -- other.com/b@v1.0.0/go.mod --
 module other.com/b