Update GitHub actions runner

Author: olivierlemasle

.github/workflows/pr-check.yaml

@@ -6,7 +6,7 @@ on:
 jobs:
   lint:
     name: Lint
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
       - name: golangci-lint
@@ -16,7 +16,7 @@ jobs:
 
   build:
     name: Test & Build
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     steps:
       - name: Setup up Go 1.x
         uses: actions/setup-go@v2

.github/workflows/release.yaml

@@ -14,7 +14,7 @@ env:
 jobs:
   push:
     name: Push images
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
 
     steps:
       - name: Check out code
@@ -67,7 +67,7 @@ jobs:
 
   release:
     name: Release
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
 
     # Run only if previous job has succeeded
     needs: [push]