chore: skip timing-sensistive AgentMetadata test in the standard suite (#7237)

* chore: skip timing-sensistive AgentMetadata test in the standard suite

* Add test-timing target

* fix windows?

* Works on my Windows desktop?

* Use tag system

* fixup! Use tag system

testutil/enable_timing.go

@@ -0,0 +1,8 @@
+//go:build timing
+
+package testutil
+
+var _ = func() any {
+	timing = true
+	return nil
+}()