ci: add ansible-core 2.18 to the test matrix (#582)

##### SUMMARY

See
https://docs.ansible.com/ansible/devel/reference_appendices/release_and_maintenance.html#ansible-core-support-matrix

.azure-pipelines/azure-pipelines.yml

@@ -47,6 +47,16 @@ stages:
             - name: Sanity
               test: devel/sanity
 
+  - stage: Sanity_2_18
+    displayName: Sanity 2.18
+    dependsOn: []
+    jobs:
+      - template: templates/matrix.yml
+        parameters:
+          targets:
+            - name: Sanity
+              test: 2.18/sanity
+
   - stage: Sanity_2_17
     displayName: Sanity 2.17
     dependsOn: []
@@ -88,6 +98,16 @@ stages:
             - name: (py3.13)
               test: devel/units/3.13
 
+  - stage: Units_2_18
+    displayName: Units 2.18
+    dependsOn: []
+    jobs:
+      - template: templates/matrix.yml
+        parameters:
+          targets:
+            - name: (py3.11)
+              test: 2.18/units/3.11
+
   - stage: Units_2_17
     displayName: Units 2.17
     dependsOn: []
@@ -130,6 +150,17 @@ stages:
             - name: (py3.13)
               test: devel/integration/3.13
 
+  - stage: Integration_2_18
+    displayName: Integration 2.18
+    dependsOn: []
+    jobs:
+      - template: templates/matrix.yml
+        parameters:
+          groups: [1, 2, 3]
+          targets:
+            - name: (py3.11)
+              test: 2.18/integration/3.11
+
   - stage: Integration_2_17
     displayName: Integration 2.17
     dependsOn: []