github: update compiler toolchains

Switch to the recently released Ubuntu 26.04 (in a container, as
github doesn't support it directly yet), Clang 22, and (still unreleased)
gcc 16. This lets us test with modern toolchains and sets the stage
for bumping the standard to C++26.

Author: avikivity

.github/workflows/test.yaml

@@ -43,6 +43,8 @@ jobs:
   test:
     timeout-minutes: 60
     runs-on: ubuntu-24.04
+    container:
+      image: docker.io/ubuntu:26.04
     steps:
       - uses: actions/checkout@v4
         with:
@@ -58,17 +60,17 @@ jobs:
       - name: Install clang++
         if: ${{ inputs.compiler == 'clang++' }}
         run: |
-          sudo apt-get -y install clang-20
+          sudo apt-get -y install clang-22
 
       - name: Install clang-scan-deps
         if: ${{ contains(inputs.enables, 'cxx-modules') }}
         run: |
-          sudo apt-get -y install clang-tools-20
+          sudo apt-get -y install clang-tools-22
 
       - name: Install g++
         if: ${{ inputs.compiler == 'g++' }}
         run: |
-          sudo apt-get -y install gcc-14 g++-14
+          sudo apt-get -y install gcc-16 g++-16
 
       - name: Install ccache
         if: ${{ inputs.enable-ccache }}
@@ -84,11 +86,11 @@ jobs:
       - name: Configure
         run: |
           if [ ${{ inputs.compiler }} = "clang++" ]; then
-            CC=clang-20
-            CPP=clang++-20
+            CC=clang-22
+            CPP=clang++-22
           else
-            CC=gcc-14
-            CPP=g++-14
+            CC=gcc-16
+            CPP=g++-16
           fi
           if ${{ inputs.enable-ccache }}; then
             MAYBE_CCACHE_OPT="--compiler-cache=ccache"