Remove macos-13 and add macos-26 runners

Author: igaztanaga

.github/workflows/ci.yml

@@ -402,15 +402,15 @@ jobs:
           #------------------
           # MacOS, clang
           #------------------
-          - toolset: clang
-            cxxstd: "11,14,17,20,2b"
-            os: macos-13
           - toolset: clang
             cxxstd: "11,14,17,20,2b"
             os: macos-14
           - toolset: clang
             cxxstd: "11,14,17,20,2b"
             os: macos-15
+          - toolset: clang
+            cxxstd: "11,14,17,20,23,2c"
+            os: macos-26
 
     timeout-minutes: 240
     runs-on: ${{matrix.os}}