Add settings.yml changes for 2.9 (#3878)

Author: AbrilRBS

reference/config_files/settings.rst

@@ -114,7 +114,7 @@ It looks like this:
            libcxx: [libstdc++, libstdc++11]
            threads: [null, posix, win32]  # Windows MinGW
            exception: [null, dwarf2, sjlj, seh]  # Windows MinGW
-           cppstd: [null, 98, gnu98, 11, gnu11, 14, gnu14, 17, gnu17, 20, gnu20, 23, gnu23]
+           cppstd: [null, 98, gnu98, 11, gnu11, 14, gnu14, 17, gnu17, 20, gnu20, 23, gnu23, 26, gnu26]
            cstd: [null, 99, gnu99, 11, gnu11, 17, gnu17, 23, gnu23]
        msvc:
            version: [170, 180, 190, 191, 192, 193, 194]
@@ -129,7 +129,7 @@ It looks like this:
                      "5.0", "6.0", "7.0", "7.1",
                      "8", "9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19"]
            libcxx: [null, libstdc++, libstdc++11, libc++, c++_shared, c++_static]
-           cppstd: [null, 98, gnu98, 11, gnu11, 14, gnu14, 17, gnu17, 20, gnu20, 23, gnu23]
+           cppstd: [null, 98, gnu98, 11, gnu11, 14, gnu14, 17, gnu17, 20, gnu20, 23, gnu23, 26, gnu26]
            runtime: [null, static, dynamic]
            runtime_type: [null, Debug, Release]
            runtime_version: [null, v140, v141, v142, v143, v144]
@@ -138,7 +138,7 @@ It looks like this:
            version: ["5.0", "5.1", "6.0", "6.1", "7.0", "7.3", "8.0", "8.1", "9.0", "9.1",
                      "10.0", "11.0", "12.0", "13", "13.0", "13.1", "14", "14.0", "15", "15.0", "16", "16.0"]
            libcxx: [libstdc++, libc++]
-           cppstd: [null, 98, gnu98, 11, gnu11, 14, gnu14, 17, gnu17, 20, gnu20, 23, gnu23]
+           cppstd: [null, 98, gnu98, 11, gnu11, 14, gnu14, 17, gnu17, 20, gnu20, 23, gnu23, 26, gnu26]
            cstd: [null, 99, gnu99, 11, gnu11, 17, gnu17, 23, gnu23]
        intel-cc:
            version: ["2021.1", "2021.2", "2021.3", "2021.4", "2022.1", "2022.2",