fix versioneer usage in pep 517 mode

Author: renefritze

.ci/common_setup.bash

@@ -17,6 +17,6 @@ git submodule update --init
 
 python -m venv ~/venv
 source ~/venv/bin/activate
-python -m pip install -U pip pytest wheel
+python -m pip install -U pip pytest wheel build
 
 python -m pip install git+https://github.com/pymor/pymor.git#egg=pymor

setup.py

@@ -2,7 +2,10 @@
 
 import os
 import pathlib
-import versioneer
+import sys
+# versioneer (+dependencies) does not work in a pep518/7 context w/o modification here
+sys.path.append(os.path.dirname(__file__))
+import versioneer  # noqa
 
 from setuptools import setup, Extension
 from setuptools import find_packages