Update Python version

Author: yuki-koyama

.github/workflows/macos-python.yml

@@ -9,7 +9,7 @@ jobs:
 
     strategy:
       matrix:
-        python-version: [ '3.8', '3.9' ]
+        python-version: [ '3.12' ]
 
     steps:
     - uses: actions/checkout@v1

.github/workflows/ubuntu-python.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-22.04]
-        python-version: [ '3.8', '3.9' ]
+        python-version: [ '3.12' ]
 
     steps:
     - uses: actions/checkout@v1

README.md

@@ -101,7 +101,7 @@ sudo apt install libeigen3-dev
 
 ## Use as a Python Library
 
-pymathtoolbox is a (sub)set of Python bindings of mathtoolbox. Tested on Python `3.8` and `3.9`.
+pymathtoolbox is a (sub)set of Python bindings of mathtoolbox. Tested on Python `3.12`.
 
 It can be installed via PyPI:
 ```