gitignore: add "venv" to ignored dirs

This is very common name for Python's virtual environments, thus used
commonly during development. Having it not ignored makes VSCode
unable to process git changes in the project.

Author: Lorak-mmk

.gitignore

@@ -18,6 +18,7 @@ docs/poetry.lock
 tests/integration/ccm
 setuptools*.tar.gz
 setuptools*.egg
+venv/
 
 cassandra/*.c
 !cassandra/cmurmur3.c