CI: Run Ameba (#4753)

This PR simply adds Ameba to the CI but doesn't actually fix any of the
detected issues.

.github/workflows/ci.yml

@@ -124,4 +124,28 @@ jobs:
       - name: Test Docker
         run: while curl -Isf http://localhost:3000; do sleep 1; done
 
+  ameba_lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: true
 
+      - name: Install Crystal
+        uses: crystal-lang/install-crystal@v1.8.0
+        with:
+          crystal: latest
+
+      - name: Cache Shards
+        uses: actions/cache@v3
+        with:
+          path: |
+            ./lib
+            ./bin
+          key: shards-${{ hashFiles('shard.lock') }}
+
+      - name: Install Shards
+        run: shards install
+
+      - name: Run Ameba linter
+        run: bin/ameba