Bump minimum python to 3.7.

.github/workflows/pythontest.yml

@@ -13,7 +13,7 @@ jobs:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
         python-version:
-          ["3.6", "3.7", "3.8", "3.9", "3.10", "3.11", pypy3]
+          ["3.7", "3.8", "3.9", "3.10", "3.11", pypy3]
         exclude:
           # sqlite3 exit handling seems to get in the way
           - os: macos-latest

setup.cfg

@@ -42,7 +42,7 @@ console_scripts =
     dulwich = dulwich.cli:main
 
 [options]
-python_requires = >=3.6
+python_requires = >=3.7
 packages =
     dulwich
     dulwich.cloud