ci: drop macos-13 (Intel) from matrix due to runner queue

GitHub-hosted macos-13 (Intel) runners have severely limited capacity
— jobs sat queued for 1h 43m on the test PR without ever starting.
Apple is winding down Intel Mac and runner availability is unlikely
to improve. Restrict the macOS coverage to macos-14 (Apple Silicon)
so the matrix is reliably green; Intel mac users can still build
locally.

Author: LimHyungTae

.github/workflows/cpp.yml

@@ -15,7 +15,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-24.04, ubuntu-22.04, windows-2022, macos-14, macos-13]
+        os: [ubuntu-24.04, ubuntu-22.04, windows-2022, macos-14]
     steps:
       - uses: actions/checkout@v4
       - name: Configure CMake

.github/workflows/pypi.yml

@@ -32,7 +32,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-22.04, windows-2022, macos-14, macos-13]
+        os: [ubuntu-22.04, windows-2022, macos-14]
 
     steps:
       - uses: actions/checkout@v4

.github/workflows/python.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-24.04, ubuntu-22.04, windows-2022, macos-14, macos-13]
+        os: [ubuntu-24.04, ubuntu-22.04, windows-2022, macos-14]
 
     steps:
       - uses: actions/checkout@v4

README.md

@@ -135,7 +135,7 @@ In addition, you can also check the paper of our baseline, Patchwork. ([arXiv][p
 ## :triangular_flag_on_post: Tested Environment
 
 - Ubuntu ~~18.04 and~~ 20.04, 22.04, and 24.04
-- macOS 13 (Intel) and macOS 14+ (Apple Silicon)
+- macOS 14+ (Apple Silicon)
 - CMake 3.25.1 (>=3.20, min. Required to install Open3D)
   - In `scripts/install_open3d.bash`, the installation of the higher version of CMake is already implemented.
 - Open3D ~~0.15.2~~ 0.18.0