CI: don't test on 3.6 (unsupported)

Author: bfontaine

.github/workflows/build.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       matrix:
         # See https://github.com/actions/python-versions/releases for available versions
-        python-version: [ "3.6", "3.7", "3.8", "3.9", "3.10", "3.11", "3.12", "3.13", "3.14" ]
+        python-version: [ "3.7", "3.8", "3.9", "3.10", "3.11", "3.12", "3.13", "3.14" ]
 
     steps:
       - name: Checkout