update upgrade test to use v1.5 (envoyproxy#6741)

[release-1.5] update upgrade test

Signed-off-by: zirain <[email protected]>

Author: zirain

test/e2e/tests/eg_upgrade.go

@@ -52,7 +52,7 @@ var EGUpgradeTest = suite.ConformanceTest{
 			chartPath := "../../../charts/gateway-helm"
 			relName := "eg"
 			depNS := "envoy-gateway-system"
-			lastVersionTag := "v1.4.0" //  the latest prior release
+			lastVersionTag := "v1.5.0" //  the latest prior release
 
 			t.Logf("Upgrading from version: %s", lastVersionTag)