chore: de-flake TestWorkspaceAgent_Metadata (round 2) (#7039)

This time, we keep the timing / "racey" tests, but avoid running
them in the harsher CI conditions.

testutil/ci.go

@@ -0,0 +1,16 @@
+package testutil
+
+import (
+	"flag"
+	"os"
+)
+
+func InCI() bool {
+	_, ok := os.LookupEnv("CI")
+	return ok
+}
+
+func InRaceMode() bool {
+	fl := flag.Lookup("race")
+	return fl != nil && fl.Value.String() == "true"
+}