bump github runner

Author: simbabque

.github/workflows/dzil-build-and-test.yml

@@ -13,7 +13,7 @@ on:
 jobs:
   build-job:
     name: Build distribution
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     container:
       image: perldocker/perl-tester:5.36
     steps:
@@ -31,7 +31,7 @@ jobs:
           path: build_dir
   coverage-job:
     needs: build-job
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     container:
       image: perldocker/perl-tester:5.36
     steps:
@@ -72,7 +72,7 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        os: [ubuntu-20.04]
+        os: [ubuntu-latest]
         perl-version:
           - "5.8"
           - "5.10"