remove support for / testing on Python 3.9

Python 3.9 will run out of upstream support 2025-10 anyway.
So we can also drop it right now and have faster CI testing.

Vagrantfile

@@ -43,7 +43,6 @@ def packages_freebsd
     pkg install -y fusefs-libs3 || true
     pkg install -y rust
     pkg install -y git bash  # fakeroot causes lots of troubles on freebsd
-    pkg install -y python39 py39-sqlite3
     pkg install -y python310 py310-sqlite3
     pkg install -y python311 py311-sqlite3 py311-pip py311-virtualenv
     # make sure there is a python3/pip3/virtualenv command

docs/development.rst

@@ -295,7 +295,7 @@ Some more advanced examples::
   # verify a changed tox.ini (run this after any change to tox.ini):
   fakeroot -u tox --recreate
 
-  fakeroot -u tox -e py39  # run all tests, but only on python 3.9
+  fakeroot -u tox -e py313  # run all tests, but only on python 3.13
 
   fakeroot -u tox borg.testsuite.locking  # only run 1 test module
 

docs/installation.rst

@@ -161,7 +161,7 @@ To install Borg from a source package (including pip), you have to install the
 following dependencies first. For the libraries you will also need their
 development header files (sometimes in a separate `-dev` or `-devel` package).
 
-* `Python 3`_ >= 3.9.0
+* `Python 3`_ >= 3.10.0
 * OpenSSL_ >= 1.1.1 (LibreSSL will not work)
 * libacl_ (which depends on libattr_)
 * libxxhash_ >= 0.8.1
@@ -446,9 +446,9 @@ If you need to use a different version of Python you can install this using ``py
 
     ...
     # create a virtual environment
-    pyenv install 3.9.0  # minimum, preferably use something more recent!
-    pyenv global 3.9.0
-    pyenv local 3.9.0
+    pyenv install 3.10.0  # minimum, preferably use something more recent!
+    pyenv global 3.10.0
+    pyenv local 3.10.0
     virtualenv --python=${pyenv which python} borg-env
     source borg-env/bin/activate   # always before using!
     ...

pyproject.toml

@@ -83,7 +83,7 @@ skip-magic-trailing-comma = true
 
 [tool.ruff]
 line-length = 120
-target-version = "py39"
+target-version = "py310"
 
 # Enable pycodestyle (`E`) and Pyflakes (`F`) codes by default.
 select = ["E", "F"]