HDDS-8523. Upgrade Github Actions runner to ubuntu-latest (#36)

diff --git a/.github/workflows/regenerate.yml b/.github/workflows/regenerate.yml
index ea6fb10..a442b7e 100644
--- a/.github/workflows/regenerate.yml
+++ b/.github/workflows/regenerate.yml
@@ -20,7 +20,7 @@
 jobs:
   build:
     name: regenerate
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
     steps:
       - name: Checkout branch with source
         uses: actions/checkout@v2