fix(ci): use C++20 for Z3 build on macOS (aggregate init with parens)

Z3 uses parenthesized aggregate initialization (e.g. key_data(k, v))
which is a C++20 feature (P0960R3). Apple Clang defaults to C++17 where
this is not supported. Switch to -std=c++20.

Assisted-By: Claude (Anthropic AI) <noreply@anthropic.com>
Signed-off-by: Paolo Dettori <dettori@us.ibm.com>

Author: pdettori

.github/workflows/kagenti-release-cli.yml

@@ -134,7 +134,7 @@ jobs:
 
       - name: Build openshell-cli
         env:
-          CXXFLAGS: "-std=c++17"
+          CXXFLAGS: "-std=c++20"
           READ_ONLY_GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: cargo build --release -p openshell-cli --features bundled-z3