chore(tox): disable sdist build (repo is not a Python package)

tox 4 tries to build an sdist from the repo root by default. With the
flat top-level layout (check-plugins/, tools/, lib/, site/, assets/,
testing/) setuptools auto-discovery trips over the "Multiple top-level
packages" check and aborts before any test environment is even set up.

Set `no_package = true` under [tox] so tox runs `deps` and `commands`
directly without touching the build backend.

Author: markuslf

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 * Fix `--require-hashes` pip install in pre-commit autoupdate workflow by using pinned version instead
+* tox.ini: disable the sdist build (`no_package = true`) so `tox` no longer trips over the flat top-level layout with "Multiple top-level packages discovered". The repo is a collection of plugin scripts, not a Python package
 * deb-updates: add missing `lib.txt` import so the "N update(s) available" summary no longer crashes with `AttributeError` at runtime
 * mysql-memory: fix `get_other_process_memory()` fallback path for psutil older than 5.3.0 (referenced an undefined `cmdline` variable and the wrong attribute on the process dict) and drop an unreachable `break` after `return` in `get_pfs_memory()`
 * mysql-storage-engines: drop a dead `SELECT ... FROM information_schema.engines` query whose result was never used

tox.ini

@@ -1,6 +1,10 @@
 [tox]
 envlist = py39, py310, py311, py312, py313, py314
 skip_missing_interpreters = true
+# this repo is not a Python package - it is a collection of check plugin scripts.
+# tell tox not to build/install an sdist from the repo root, otherwise setuptools
+# auto-discovery trips over the top-level lib/, site/, assets/ and testing/ dirs.
+no_package = true
 
 [testenv]
 deps =