fix(insomnia-test): remove isVisible/innerText race when reading variable modal

readVariableModal checked row.isVisible() then awaited row.innerText(); when the
async Source recompute unmounted the row in between, innerText waited 30s.
Read an atomic DOM snapshot and wait for it to settle, and wait for the custom
template preview in the modal-editing spec.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

packages/insomnia-test/tests/environment/variable-source-live-preview/variable-source-modal-editing.spec.ts

@@ -30,7 +30,10 @@ test("Verify the tag modal's source follows the edited template and hides for no
     "{{ _.subOnlyVar }}",
     "subOnly_base",
   );
-  await variableSourceFlow.selectModalVariable({ label: "-- Custom --" });
+  await variableSourceFlow.selectModalVariable(
+    { label: "-- Custom --" },
+    "my%20custom%20template%20logic",
+  );
   const plainText = await variableSourceFlow.setModalTemplate("plain text", "plain text");
   const inheritedKey = await variableSourceFlow.setModalTemplate("{{ constructor }}");
   const padded = await variableSourceFlow.setModalTemplate("{{  _.subOnlyVar  }}", "subOnly_base");