GHA: Remove C++2b test from clang-16/17 on ubuntu-24.04

Author: Flamefire

.github/workflows/ci.yml

@@ -128,12 +128,12 @@ jobs:
             install: clang-15
           - toolset: clang
             compiler: clang++-16
-            cxxstd: "03,11,14,17,20,2b"
+            cxxstd: "03,11,14,17,20"
             os: ubuntu-24.04
             install: clang-16
           - toolset: clang
             compiler: clang++-17
-            cxxstd: "03,11,14,17,20,2b"
+            cxxstd: "03,11,14,17,20"
             os: ubuntu-24.04
             install: clang-17
           - toolset: clang