ci : bump setup-python to v6

Author: beachdweller

.github/workflows/check_links.yml

@@ -16,7 +16,7 @@ jobs:
       uses: actions/checkout@v4
 
     - name: Set up Python
-      uses: actions/setup-python@v5
+      uses: actions/setup-python@v6
       with:
         python-version: '3.11'
 

.github/workflows/conda_env_test.yml

@@ -26,7 +26,7 @@ jobs:
       uses: actions/checkout@v4
 
     - name: Set up Python
-      uses: actions/setup-python@v5
+      uses: actions/setup-python@v6
       with:
         python-version: '3.11'