fix: Add missing space in dictionary comprehension

A space was missing between the value and `for`. For example:

```python
import tempfile
import sys
import griffe

with tempfile.TemporaryDirectory() as tmp:
    sys.path.insert(0, tmp)
    with open(f"{tmp}/test_for_griffe.py", "x") as f:
        print("A = {key: value for key, value in []}", file=f)

    module = griffe.load("test_for_griffe")
    print(module.get_member("A").value)
```

...displayed:

```python
{key: valuefor (key, value) in []}
```

Add the missing space.

Issue-mkdocstrings-python-311: mkdocstrings/python#311
PR-420: #420

Author: niooss-ledger

src/griffe/_internal/expressions.py

@@ -473,6 +473,7 @@ def iterate(self, *, flat: bool = True) -> Iterator[str | Expr]:
         yield from _yield(self.key, flat=flat)
         yield ": "
         yield from _yield(self.value, flat=flat)
+        yield " "
         yield from _join(self.generators, " ", flat=flat)
         yield "}"
 

tests/test_expressions.py

@@ -231,3 +231,14 @@ def func[Z](arg1: T, arg2: Y): pass
 
         assert module["C.func"].parameters["arg1"].annotation.canonical_path == "module.C[T]"
         assert module["C.func"].parameters["arg2"].annotation.canonical_path == "Y"
+
+
+@pytest.mark.xfail(reason="Tuple in comprehension target is not yet implicit")
+def test_render_dict_comprehension() -> None:
+    """Assert dict comprehensions are rendered correctly."""
+    with temporary_visited_module(
+        """
+        d = {k: v for k, v in items if k}
+        """,
+    ) as module:
+        assert str(module["d"].value) == "{k: v for k, v in items if k}"