Add nightly on CI

LTS-19 and GHC-9.2 is coming. Adding this to ensure we can compile,
which seems to be the case.

We are only disabled in Stackage because hoauth2 is not ready, for which
I've opened: https://github.com/freizl/hoauth2/issues/142

.github/workflows/ci.yml

@@ -41,3 +41,16 @@ jobs:
       - uses: rwe/actions-hlint-run@v2
         with:
           fail-on: warning
+
+  nightly:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+      - uses: freckle/stack-cache-action@v2
+        with:
+          stack-yaml: stack-nightly.yaml
+      - uses: freckle/stack-action@v3
+        with:
+          stack-yaml: stack-nightly.yaml
+          stack-arguments: --resolver nightly

stack-nightly.yaml

@@ -0,0 +1,11 @@
+resolver: 2022-03-25
+
+extra-deps:
+  - hoauth2-2.3.0
+  - yesod-auth-1.6.11
+  - yesod-core-1.6.22.0
+  - yesod-form-1.7.0
+  - yesod-persistent-1.6.0.7
+
+# binary-0.8.9.0 and bytestring-0.11.3.0 are too new for hoauth2-2.3.0
+allow-newer: true