CI: Specify Ubuntu 22.04-LTS for host

Author: jserv

.github/workflows/main.yml

@@ -4,7 +4,7 @@ on: [push, pull_request]
 
 jobs:
   rv32emu:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
     - uses: actions/checkout@v3.0.2
     - name: install-dependencies
@@ -17,7 +17,7 @@ jobs:
       run: make check
 
   coding_style:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
     - uses: actions/checkout@v3.0.2
     - name: coding convention