Update CI target OSes

Remove platforms deprecated by GitHub Actions
Add new platforms supported by the same

.github/workflows/testing.yml

@@ -7,7 +7,7 @@ jobs:
   unix-testing:
     strategy:
       matrix:
-        os: [ubuntu-20.04, ubuntu-18.04, macos-11.0, macos-10.15]
+        os: [ubuntu-20.04, ubuntu-22.04, macos-11, macos-12]
         cc: [gcc, clang]
         buildsys: [make, cmake]
         exclude:
@@ -64,6 +64,7 @@ jobs:
     strategy:
       matrix:
         bits: [32, 64]
+        os: [windows-2019, windows-2022]
         include:
           - bits: 32
             arch: x86
@@ -72,7 +73,7 @@ jobs:
             arch: x86_x64
             platform: x64
       fail-fast: false
-    runs-on: windows-2019
+    runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2
       - name: Get zlib, libpng and bison
@@ -149,7 +150,6 @@ jobs:
     strategy:
       matrix:
         bits: [32, 64]
-        os: [ubuntu-18.04]
         include:
           - bits: 32
             arch: i686
@@ -158,7 +158,7 @@ jobs:
             arch: x86-64
             triplet: x86_64-w64-mingw32
       fail-fast: false
-    runs-on: ${{ matrix.os }}
+    runs-on: ubuntu-latest
     env:
       DIST_DIR: win${{ matrix.bits }}
     steps:
@@ -205,9 +205,10 @@ jobs:
     needs: windows-xbuild
     strategy:
       matrix:
+        os: [windows-2019, windows-2022]
         bits: [32, 64]
       fail-fast: false
-    runs-on: windows-2019
+    runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2
       - name: Retrieve binaries