fix: fix edge case with pydantic errors

this shows:
```
checking registry/poap/calldata-PoapBridge.json...
ERROR: Validation error: {'type': 'json_invalid', 'loc': (), 'msg': 'Invalid JSON: expected value at line 1 column 1', 'input':
'Missing/Invalid API Key', 'ctx': {'error': 'expected value at line 1 column 1'}}
```

instead of:
```
checking registry/poap/calldata-PoapBridge.json...
Error: Invalid JSON: expected value at line 1 column 1
```

src/erc7730/lint/lint.py

@@ -82,7 +82,10 @@ def lint_file(path: Path, linter: ERC7730Linter, out: OutputAdder) -> None:
     except ValidationError as e:
         for ex in e.errors(include_url=False, include_context=True, include_input=True):
             loc = ex["loc"]
-            adder.error(title=f"{loc} is invalid", message=ex["msg"])
+            if loc == ():
+                adder.error(title="Validation error", message=str(ex))
+            else:
+                adder.error(title=f"{loc} is invalid", message=ex["msg"])
     except Exception as e:
         # TODO unwrap pydantic validation errors here to provide more user-friendly error messages
         adder.error(title="Failed to parse descriptor", message=str(e))

tests/model/test_model_serialization.py

@@ -20,6 +20,9 @@ def test_schema(input_file: Path) -> None:
     """Test model serializes to JSON that matches the schema."""
     assert_valid_erc_7730(InputERC7730Descriptor.load(input_file))
 
+def test_poap() -> None:
+    """Test model serializes to JSON that matches the schema."""
+    InputERC7730Descriptor.load(Path("/home/jnicoulaud/work/ledger/backend/cal/python-erc7730/python-erc7730-1/tests/registries/clear-signing-erc7730-registry/registry/poap/calldata-PoapBridge.json"))
 
 @pytest.mark.parametrize("input_file", ERC7730_DESCRIPTORS, ids=path_id)
 def test_round_trip(input_file: Path) -> None: