doc/conf: use importlib.metadata in favor of pkg_resources

Since Python 3.12, setuptools is no longer pre-installed in virtual envs
created with venv [1].

The used alternative `importlib.metadata` is available for
Python >=3.8 [2].

[1] https://docs.python.org/3/library/venv.html#module-venv
[2] https://docs.python.org/3.12/library/importlib.metadata.html

Signed-off-by: Leonardo Mörlein <git@irrelefant.net>
[bst: rephrased commit message]
(cherry picked from commit 34215b9)

Author: lemoer

doc/conf.py

@@ -21,7 +21,7 @@
 import sys
 sys.path.insert(0, os.path.abspath('..'))
 
-from pkg_resources import get_distribution
+from importlib.metadata import version
 
 # Import read_the_docs theme
 import sphinx_rtd_theme
@@ -65,7 +65,7 @@
 # built documents.
 #
 # The full version, including alpha/beta/rc tags.
-release = get_distribution('labgrid').version
+release = version('labgrid')
 # The short X.Y version.
 version = '.'.join(release.split('.')[:2])