Fix build and installation issues on Gentoo

Make minigalaxy successfully install by running either `pip install .`
or by running setup.py directly.

Make sure all test packages are excluded from the installation process [1].

Use the regular build backend instead of the fallback [2]. Make the
regular backend work by appending the current directory to Python PATH.
This way we can pass the package version to setuptools [3].

[1]: https://projects.gentoo.org/python/guide/qawarn.html#example-for-test-packages-installed-by-setuptools
[2]: https://projects.gentoo.org/python/guide/qawarn.html#setuptools-build-meta-legacy
[3]: pypa/setuptools#3939 (comment)

Author: viacheslavka

pyproject.toml

@@ -16,5 +16,5 @@ dynamic= [
 ]
 
 [build-system]
-requires = ["setuptools", "wheel"]
-build-backend = "setuptools.build_meta:__legacy__"
+requires = ["setuptools"]
+build-backend = "setuptools.build_meta"

setup.py

@@ -2,7 +2,10 @@
 from glob import glob
 import subprocess
 import os
-from minigalaxy.version import VERSION
+import sys
+
+sys.path.insert(0, os.getcwd())
+from minigalaxy.version import VERSION  # noqa: E402
 
 # Generate the translations
 subprocess.run(['bash', 'scripts/compile-translations.sh'])
@@ -15,7 +18,7 @@
 setup(
     name="minigalaxy",
     version=VERSION,
-    packages=find_packages(exclude=['tests']),
+    packages=find_packages(exclude=['tests', 'tests.*']),
     scripts=['bin/minigalaxy'],
 
     data_files=[