Fix issue with DEP004 being raised incorrectly if a dependency is bot…

…h a regular and a dev dependency

deptry/issues_finder/misplaced_dev.py

@@ -43,7 +43,9 @@ def find(self) -> list[Violation]:
         return misplaced_dev_dependencies
 
     def _is_development_dependency(self, module: Module, corresponding_package_name: str) -> bool:
-        if not module.is_dev_dependency:
+        # Module can both be a regular and a development dependency.
+        # Only continue if module is ONLY a dev dependency.
+        if not module.is_dev_dependency or module.is_dependency:
             return False
 
         if module.name in self.ignored_modules:

tests/unit/issues_finder/test_misplaced_dev.py

@@ -20,3 +20,19 @@ def test_simple() -> None:
     assert MisplacedDevDependenciesFinder(modules_locations, dependencies).find() == [
         MisplacedDevDependencyViolation(module_foo, location) for location in module_foo_locations
     ]
+
+
+def test_regular_and_dev_dependency() -> None:
+    """
+    If a dependency is both a regular and a development dependency, no error 'misplaced dev dependency' violation
+    should be detected if it is used in the code base.
+    """
+
+    dependencies = [Dependency("foo", Path("pyproject.toml"))]
+
+    module_foo_locations = [Location(Path("foo.py"), 1, 2)]
+    module_foo = Module("foo", dev_top_levels=["foo"], is_dev_dependency=True, is_dependency=True)
+
+    modules_locations = [ModuleLocations(module_foo, module_foo_locations)]
+
+    assert not MisplacedDevDependenciesFinder(modules_locations, dependencies).find()