Add package extensions to test_stale_deps docstring (#203)

* Add package extensions to `test_stale_deps` docstring

* Add changelog

* Update src/stale_deps.jl

Author: lgoettgens

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- The docstring for `test_stale_deps` explains the situation with package extensions. ([#203](https://github.com/JuliaTesting/Aqua.jl/pull/203))
+
 
 ## [0.7.3] - 2023-09-25
 

src/stale_deps.jl

@@ -5,7 +5,14 @@ Test that `package` loads all dependencies listed in `Project.toml`.
 Note that this does not imply that `package` loads the dependencies
 directly, this can be achieved via transitivity as well.
 
-!!! note "Known bug"
+!!! note "Weak dependencies and extensions"
+
+    Due to the automatic loading of package extensions once all of
+    their trigger dependencies are loaded, Aqua.jl can, by design of julia,
+    not check if a package extension indeed loads all of its trigger
+    dependencies using `import` or `using`. 
+
+!!! warning "Known bug"
 
     Currently, `Aqua.test_stale_deps` does not detect stale
     dependencies when they are stdlib.  This is considered a bug and