vagrant: pyenv: only install python 3.12

on macOS, installing older Pythons seems to uninstall OpenSSL 3 and only 1.1 is left.

also, building all these pythons and misc. openssl versions takes forever and we
only need 3.12 for the binary build. testing on misc. python versions is regularly
done one github actions CI.

Vagrantfile

@@ -169,9 +169,6 @@ def install_pythons(boxname)
     . ~/.bash_profile
     echo "PYTHON_CONFIGURE_OPTS: ${PYTHON_CONFIGURE_OPTS}"
     pyenv install 3.12.4  # tests, binary build (3.12.5/6/7 has a broken pip on old macOS)
-    pyenv install 3.11.3  # tests
-    pyenv install 3.10.2  # tests
-    pyenv install 3.9.4  # tests
     pyenv rehash
   EOF
 end
@@ -236,8 +233,8 @@ def run_tests(boxname, skip_env)
     . ../borg-env/bin/activate
     if which pyenv 2> /dev/null; then
       # for testing, use the earliest point releases of the supported python versions:
-      pyenv global 3.9.4 3.10.2 3.11.3 3.12.4
-      pyenv local 3.9.4 3.10.2 3.11.3 3.12.4
+      pyenv global 3.12.4
+      pyenv local 3.12.4
     fi
     # otherwise: just use the system python
     # some OSes can only run specific test envs, e.g. because they miss FUSE support: