Make run_tests.sh find where pyxcrypt was installed

It is possible that on different linux distributions
it can be placed with different prefix
(purelib, platlib)

Author: Daniel Zagaynov

tests/run_tests.sh

@@ -3,4 +3,4 @@
 mkdir -p /tmp/test_env
 meson compile
 DESTDIR=/tmp/test_env meson install
-PYTHONPATH=/tmp/test_env/usr/local/lib/python3/site-packages:/tmp/test_env/usr/local/lib64/python3/site-packages python3 -P -m unittest discover -s "$1" -v
+PYTHONPATH=$(find /tmp/test_env -name pyxcrypt -printf %h) python3 -P -m unittest discover -s "$1" -v