Revert "ci: disable infection since it segfaults in GA (#138)"

This reverts commit 1cd6284.

.github/workflows/infection.yaml

@@ -0,0 +1,32 @@
+name: Infection
+
+on:
+  pull_request:
+  push:
+    branches:
+      - "*.*.x"
+
+jobs:
+  Infection:
+    runs-on: ubuntu-20.04
+
+    steps:
+      - name: "Checkout"
+        uses: actions/checkout@v3
+        with:
+          fetch-depth: 2
+
+      - name: "Install PHP"
+        uses: "shivammathur/setup-php@v2"
+        with:
+          php-version: 8.1
+          coverage: "pcov"
+
+      - name: "Install dependencies with Composer"
+        uses: "ramsey/composer-install@v2"
+
+      - name: Run Infection
+        run: vendor/bin/roave-infection-static-analysis-plugin --threads=$(nproc)
+        env:
+          STRYKER_DASHBOARD_API_KEY: ${{ secrets.STRYKER_DASHBOARD_API_KEY }}
+