CI: use macos-26

the Github runner is out of beta

.github/workflows/tests.yml

@@ -6,11 +6,12 @@ jobs:
       fail-fast: false
       matrix:
         os:
-          - ubuntu-24.04
           - ubuntu-22.04
-          - macos-15-intel
-          - macos-15
+          - ubuntu-24.04
           - macos-14
+          - macos-15
+          - macos-15-intel
+          - macos-26
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2