Fix Consul versions in nightly 1.19 int tests (#21226)

We should be testing against n-2 + LTS, so we need to replace 1.16 with 1.18.

.github/workflows/nightly-test-integrations-1.19.x.yml

@@ -204,7 +204,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        consul-version: ["1.15", "1.16", "1.17"]
+        consul-version: ["1.15", "1.17", "1.18"]
     env:
       CONSUL_LATEST_VERSION: ${{ matrix.consul-version }}
       ENVOY_VERSION: "1.24.6"
@@ -330,7 +330,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        consul-version: [ "1.15", "1.16", "1.17"]
+        consul-version: ["1.15", "1.17", "1.18"]
     env:
       CONSUL_LATEST_VERSION: ${{ matrix.consul-version }}
     steps: