fix(tests): cover regex matches in silence tests

ui/src/Components/Grid/AlertGrid/AlertGroup/Silence/__snapshots__/index.test.js.snap

@@ -112,6 +112,9 @@ exports[`<Silence /> matches snapshot with expaned details 1`] = `
     <span class=\\"badge badge-success text-nowrap text-truncate px-1 mr-1\\">
       alertname=MockAlert
     </span>
+    <span class=\\"badge badge-success text-nowrap text-truncate px-1 mr-1\\">
+      instance=~foo[0-9]+
+    </span>
   </div>
 </div>
 "

ui/src/Components/Grid/AlertGrid/AlertGroup/Silence/index.test.js

@@ -30,6 +30,11 @@ const silence = {
       name: "alertname",
       value: "MockAlert",
       isRegex: false
+    },
+    {
+      name: "instance",
+      value: "foo[0-9]+",
+      isRegex: true
     }
   ],
   startsAt: "2000-01-01T10:00:00Z",