fix(e2e): nil-guard port-forward kill, remove sleep, align GO_VERSION with go.mod

Author: syscod3

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ on:
     branches: [main]
 
 env:
-  GO_VERSION: "1.24"
+  GO_VERSION: "1.25"
 
 jobs:
   lint:

test/e2e/e2e_test.go

@@ -127,10 +127,13 @@ spec:
 				fmt.Sprintf("svc/%s-operator", helmRelease),
 				"18080:8080", "-n", namespace)
 			Expect(pf.Start()).To(Succeed())
-			defer pf.Process.Kill() //nolint:errcheck
-
-			time.Sleep(2 * time.Second)
+			DeferCleanup(func() {
+				if pf.Process != nil {
+					_ = pf.Process.Kill()
+				}
+			})
 
+			// Eventually handles connection-refused while port-forward is starting up.
 			Eventually(func(g Gomega) {
 				resp, err := http.Get("http://localhost:18080/metrics") //nolint:noctx
 				g.Expect(err).NotTo(HaveOccurred())