[Chore] Update Stackage resolver and Stack version on CI

Problem: there is a newer LTS version than specified in stack.yaml,
and a newer Stack version than specified in the CI config.
It's not a problem per-se, but it's a good practice to update
all versions from time to time.

Solution:
1. Update the resolver in stack.yaml to the latest LTS one at the
moment of doing this change (lts-22.4).
2. Update Stack version in ci.yml to the latest released one (2.13.1).
3. Update the GHC version there to match the one implied by the
resolver.

.github/workflows/ci.yml

@@ -90,8 +90,8 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        stack: ["2.9.3"]
-        ghc: ["9.4.5"]
+        stack: ["2.13.1"]
+        ghc: ["9.6.3"]
 
     steps:
     - uses: actions/checkout@v4

stack.yaml

@@ -1 +1 @@
-resolver: lts-21.0
+resolver: lts-22.4

stack.yaml.lock

@@ -6,7 +6,7 @@
 packages: []
 snapshots:
 - completed:
-    sha256: 1867d84255dff8c87373f5dd03e5a5cb1c10a99587e26c8793e750c54e83ffdc
-    size: 639139
-    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/21/0.yaml
-  original: lts-21.0
+    sha256: 8b211c5a6aad3787e023dfddaf7de7868968e4f240ecedf14ad1c5b2199046ca
+    size: 714097
+    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/22/4.yaml
+  original: lts-22.4