Bump ubuntu-18.04 -> ubuntu-22.04

.github/workflows/ci.yml

@@ -6,7 +6,7 @@ on:
 
 jobs:
   build-linux-gcc:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v1
       - name: install dependencies
@@ -19,7 +19,7 @@ jobs:
         env:
           CC: gcc
   build-linux-clang:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v1
       - name: install dependencies