Add Python 3.13 (default) replacement jobs for removed 3.13t jobs

After removing Python 3.13t support (incompatible with PyCriticalSection_BeginMutex
which requires Python 3.14+), we're adding replacement jobs using Python 3.13
(default) to maintain test coverage in key dimensions:

1. ubuntu-latest, Python 3.13: C++20 + DISABLE_HANDLE_TYPE_NAME_DEFAULT_IMPLEMENTATION
   - Replaces: ubuntu-latest, 3.13t with same config
   - Maintains coverage for this specific configuration combination

2. macos-15-intel, Python 3.13: C++11
   - Replaces: macos-15-intel, 3.13t with same config
   - Maintains macOS coverage for Python 3.13

3. manylinux (musllinux), Python 3.13: GIL testing
   - Replaces: manylinux, 3.13t job
   - Maintains manylinux/musllinux container testing coverage

These additions are proposed to get feedback on which jobs should be kept
to maintain appropriate test coverage without the experimental 3.13t builds.

Author: rwgk

.github/workflows/ci.yml

@@ -83,6 +83,9 @@ jobs:
           - runs-on: ubuntu-latest
             python-version: '3.12'
             cmake-args: -DPYBIND11_TEST_SMART_HOLDER=ON -DPYBIND11_SIMPLE_GIL_MANAGEMENT=ON
+          - runs-on: ubuntu-latest
+            python-version: '3.13'
+            cmake-args: -DCMAKE_CXX_STANDARD=20 -DPYBIND11_DISABLE_HANDLE_TYPE_NAME_DEFAULT_IMPLEMENTATION=ON
           - runs-on: ubuntu-latest
             python-version: '3.14'
             cmake-args: -DCMAKE_CXX_STANDARD=14
@@ -99,6 +102,9 @@ jobs:
           - runs-on: macos-15-intel
             python-version: '3.11'
             cmake-args: -DPYBIND11_TEST_SMART_HOLDER=ON
+          - runs-on: macos-15-intel
+            python-version: '3.13'
+            cmake-args: -DCMAKE_CXX_STANDARD=11
           - runs-on: macos-latest
             python-version: '3.12'
             cmake-args: -DCMAKE_CXX_STANDARD=17 -DPYBIND11_DISABLE_HANDLE_TYPE_NAME_DEFAULT_IMPLEMENTATION=ON
@@ -230,6 +236,32 @@ jobs:
       run: cmake --build . --target test_cross_module_rtti
 
 
+  manylinux:
+    name: Manylinux on 🐍 3.13 • GIL
+    if: github.event.pull_request.draft == false
+    runs-on: ubuntu-latest
+    timeout-minutes: 40
+    container: quay.io/pypa/musllinux_1_2_x86_64:latest
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+
+      - name: Prepare uv's path
+        run: echo "$HOME/.local/bin" >> $GITHUB_PATH
+
+      - name: Install ninja
+        run: uv tool install ninja
+
+      - name: Configure via preset
+        run: cmake --preset venv -DPYBIND11_CREATE_WITH_UV=python3.13
+
+      - name: Build C++11
+        run: cmake --build --preset venv
+
+      - name: Python tests C++11
+        run: cmake --build --preset testsvenv -t pytest
+
   deadsnakes:
     if: github.event.pull_request.draft == false
     strategy: