Add heroku-26 to hatchet CI matrix

Author: Malax

.github/workflows/ci.yml

@@ -33,7 +33,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        stack: ["heroku-22", "heroku-24"]
+        stack: ["heroku-22", "heroku-24", "heroku-26"]
     env:
       HATCHET_APP_LIMIT: 100
       PARALLEL_SPLIT_TEST_PROCESSES: 8