Build OTP on Ubuntu focal

.github/workflows/ci.yml

@@ -1,12 +1,12 @@
 name: CI
 on:
   push:
-    branches: [main]
+    branches: [focal]
 env:
   OTP_RELEASE: 22.0.7
 jobs:
   create_release:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     outputs:
       upload_url: ${{ steps.create_release.outputs.upload_url }}
     steps:
@@ -23,7 +23,7 @@ jobs:
   build_and_upload:
     strategy:
       matrix:
-        platform: [ubuntu-18.04, macos-10.15]
+        platform: [ubuntu-20.04, macos-10.15]
         wx: [headless, graphical]
         src: [src, no-src]
     runs-on: ${{ matrix.platform }}

README.md

@@ -1,2 +1,2 @@
 # otp_bin
-This repository uses github actions and `kerl` (https://github.com/kerl/kerl) to compile erlang/OTP for linux (ubuntu 18.04) and macos.
+This repository uses github actions and `kerl` (https://github.com/kerl/kerl) to compile erlang/OTP for linux (ubuntu 20.04) and macos.