Avoid falsely marking non-submodules as submodule aliases (#6182)

## Summary

We have some code to ensure that if an aliased import is used, any
submodules should be marked as used too. This comment says it best:

```rust
// If the name of a submodule import is the same as an alias of another import, and the
// alias is used, then the submodule import should be marked as used too.
//
// For example, mark `pyarrow.csv` as used in:
//
// ```python
// import pyarrow as pa
// import pyarrow.csv
// print(pa.csv.read_csv("test.csv"))
// ```
```

However, it looks like when we go to look up `pyarrow` (of `import
pyarrow as pa`), we aren't checking to ensure the resolved binding is
_actually_ an import. This was causing us to attribute `print(rm.ANY)`
to `def requests_mock` here:

```python
import requests_mock as rm

def requests_mock(requests_mock: rm.Mocker):
    print(rm.ANY)
```

Closes https://github.com/astral-sh/ruff/issues/6180.

crates/ruff/resources/test/fixtures/pyflakes/F823.py

@@ -63,3 +63,10 @@ def main():
 
     for sys in range(5):
         pass
+
+
+import requests_mock as rm
+
+
+def requests_mock(requests_mock: rm.Mocker):
+    print(rm.ANY)

crates/ruff_python_semantic/src/model.rs

@@ -594,7 +594,12 @@ impl<'a> SemanticModel<'a> {
             return None;
         }
 
-        self.scopes[scope_id].get(qualified_name)
+        let binding_id = self.scopes[scope_id].get(qualified_name)?;
+        if !self.bindings[binding_id].kind.is_submodule_import() {
+            return None;
+        }
+
+        Some(binding_id)
     }
 
     /// Resolves the [`Expr`] to a fully-qualified symbol-name, if `value` resolves to an imported