Update github workflows to use ubuntu-20.04

.github/workflows/blank.yml

diff --git a/.github/workflows/blank.yml b/.github/workflows/blank.yml
index b0b167c..0db7ea6 100644
--- a/.github/workflows/blank.yml
+++ b/.github/workflows/blank.yml
@@ -18,7 +18,7 @@
   # This workflow contains a single job called "build"
   build:
     # The type of runner that the job will run on
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
 
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps: