🐛 Fix py config merger module list issue

Apart from the already supported override:
```
[[tool.mypy.overrides]]
module = "some.module.name"
```

mypy also supports overringing multiple modules at once:
```
[[tool.mypy.overrides]]
module = ["some.module.name", "some.other.module.name"]
```

Made the non-list case into a list to have a uniform handling of it.
Also made it merge the different overrides of the same module.

CHANGELOG.md

@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+- Python's config merger now handles mypy overrides targeting multiple packages.
+
 ## [5.0.0] - 2024-10-15
 
 ### Added

python/hooks/config-merger.py

@@ -82,12 +82,12 @@ def mypy_overrides(config_file, key) -> dict:
 
     root = {}
     for override in overrides:
-        module_name = f'mypy-{override.pop("module")}'
-        root.update(
-            {
-                module_name: override,
-            }
-        )
+        modules = override.pop("module")
+        if not isinstance(modules, list):
+            modules = [modules]
+        for module in modules:
+            module_name = f'mypy-{module}'
+            root.setdefault(module_name, {}).update(override)
     to_remove = config_file
     for remove_key in keys[:-1]:
         to_remove = to_remove.get(remove_key)