ci: refresh GitHub Actions matrix

 * Add ubuntu-22.04, remove 18.04
 * Add macos-12, remove 10.15

Change-Id: Iffdf6b6ff25da8f62ca2bede821dcc9969475c7b
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 15841e6..3495a8f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -13,18 +13,22 @@
 jobs:
   linux:
     name: ${{ matrix.compiler }} on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
       matrix:
-        compiler: [g++-8, g++-9, g++-10, g++-11,
-                   clang++-7, clang++-8, clang++-9, clang++-10, clang++-11, clang++-12]
         os: [ubuntu-20.04]
+        compiler: [g++-7, g++-8, g++-9, g++-10,
+                   clang++-7, clang++-8, clang++-9, clang++-10, clang++-11, clang++-12]
         include:
-          - compiler: g++-7
-            os: ubuntu-18.04
-          - compiler: clang++-6.0
-            os: ubuntu-18.04
-    runs-on: ${{ matrix.os }}
+          - os: ubuntu-22.04
+            compiler: g++-11
+          - os: ubuntu-22.04
+            compiler: g++-12
+          - os: ubuntu-22.04
+            compiler: clang++-13
+          - os: ubuntu-22.04
+            compiler: clang++-14
     env:
       CXX: ${{ matrix.compiler }}
     steps:
@@ -39,17 +43,15 @@
 
   macos:
     name: Xcode ${{ matrix.xcode }} on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
       matrix:
-        xcode: ['11.3', '11.7', '12.4']
-        os: [macos-10.15]
+        os: [macos-11]
+        xcode: ['12.4', '12.5', '13.2']
         include:
-          - xcode: '12.5'
-            os: macos-11
-          - xcode: '13.2'
-            os: macos-11
-    runs-on: ${{ matrix.os }}
+          - os: macos-12
+            xcode: '13.4'
     steps:
       - name: Set up Xcode
         uses: maxim-lobanov/setup-xcode@v1