Drop support for Python 3.5

Running repo with Python 3.5 fails due to the use of the encoding
parameter to subprocess.run(). There are also f-strings being used in
some of the tests.

This drops support for these systems:
* Ubuntu Xenial: released Apr 2016, EOS Apr 2021, EOL Apr 2024
* Debian Stretch: released Jun 2017, EOL Jun 2022

So the minimum required distros now are:
* Ubuntu Bionic: released Apr 2018 w/Python 3.6
* Debian Buster: released Jul 2019 w/Python 3.7

Change-Id: I1144f7ab6f882b10cac0131982df081fe4ac44f9
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/303363
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>

.github/workflows/test-ci.yml

@@ -14,7 +14,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        python-version: [3.5, 3.6, 3.7, 3.8, 3.9]
+        python-version: [3.6, 3.7, 3.8, 3.9]
     runs-on: ${{ matrix.os }}
 
     steps:

main.py

@@ -71,7 +71,7 @@ from subcmds import all_commands
 #
 # python-3.6 is in Ubuntu Bionic.
 MIN_PYTHON_VERSION_SOFT = (3, 6)
-MIN_PYTHON_VERSION_HARD = (3, 5)
+MIN_PYTHON_VERSION_HARD = (3, 6)
 
 if sys.version_info.major < 3:
   print('repo: error: Python 2 is no longer supported; '

requirements.json

@@ -38,9 +38,9 @@
   # Supported Python versions.
   #
   # python-3.6 is in Ubuntu Bionic.
-  # python-3.5 is in Debian Stretch.
+  # python-3.7 is in Debian Buster.
   "python": {
-    "hard": [3, 5],
+    "hard": [3, 6],
     "soft": [3, 6]
   },
 

setup.py

@@ -56,6 +56,6 @@ setuptools.setup(
         'Programming Language :: Python :: 3 :: Only',
         'Topic :: Software Development :: Version Control :: Git',
     ],
-    python_requires='>=3.5',
+    python_requires='>=3.6',
     packages=['subcmds'],
 )

tox.ini

@@ -15,11 +15,10 @@
 # https://tox.readthedocs.io/
 
 [tox]
-envlist = py35, py36, py37, py38, py39
+envlist = py36, py37, py38, py39
 
 [gh-actions]
 python =
-    3.5: py35
     3.6: py36
     3.7: py37
     3.8: py38