diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b002263a0..5a84262f8 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -15,7 +15,7 @@ env:
 
 jobs:
   build:
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
       matrix:
@@ -108,7 +108,7 @@ jobs:
         run: composer test
 
   coding-standard:
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-20.04
     name: Coding Standard
     steps:
       - name: "Checkout"
@@ -136,7 +136,7 @@ jobs:
         run: composer check-cs
 
   benchmark:
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-20.04
     name: Benchmark
     steps:
       - name: "Checkout"
@@ -164,7 +164,7 @@ jobs:
         run: composer bench
 
   static-analysis:
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-20.04
     name: "Static analysis"
     steps:
       - name: "Checkout"
@@ -192,7 +192,7 @@ jobs:
         run: composer static-analysis
 
   coverage:
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-20.04
     name: "Coverage"
     steps:
       - name: "Checkout"
diff --git a/tests/Functional/TestCase.php b/tests/Functional/TestCase.php
index 1426d3b33..c9c914da8 100644
--- a/tests/Functional/TestCase.php
+++ b/tests/Functional/TestCase.php
@@ -9,6 +9,7 @@
 use Symfony\Bundle\FrameworkBundle\Client;
 use Symfony\Bundle\FrameworkBundle\KernelBrowser;
 use Symfony\Bundle\FrameworkBundle\Test\WebTestCase;
+use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\Filesystem\Filesystem;
 use Symfony\Component\HttpFoundation\Request;
 
@@ -90,7 +91,7 @@ protected static function assertGraphQL(string $query, array $expectedData = nul
         static::assertSame($expected, $result, \json_encode($result));
     }
 
-    protected static function getContainer()
+    protected static function getContainer(): ContainerInterface
     {
         return static::$kernel->getContainer();
     }