Update Python version to 3.13 in CI workflows

Changed the PYTHON_VERSION from 3.13.6 to 3.13 in the Linux, macOS, and Windows GitHub Actions workflows to use the latest 3.13.x release.

.github/workflows/build-linux.yml

@@ -9,7 +9,7 @@ permissions:
   contents: write
 
 env:
-  PYTHON_VERSION: '3.13.6'
+  PYTHON_VERSION: '3.13'
 
 jobs:
   build-linux:

.github/workflows/build-macos.yml

@@ -9,7 +9,7 @@ permissions:
   contents: write
 
 env:
-  PYTHON_VERSION: '3.13.6'
+  PYTHON_VERSION: '3.13'
 
 jobs:
   build-macos:

.github/workflows/build-windows.yml

@@ -9,7 +9,7 @@ permissions:
   contents: write
 
 env:
-  PYTHON_VERSION: '3.13.6'
+  PYTHON_VERSION: '3.13'
 
 jobs:
   build-windows: