Remove python_version mypy configuration; fix issues arising on 3.11-3.14

Author: akx

Tests/conftest.py

@@ -10,7 +10,7 @@
 
 gil_enabled_at_start = True
 if FREE_THREADED_BUILD:
-    gil_enabled_at_start = sys._is_gil_enabled()  # type: ignore[attr-defined]
+    gil_enabled_at_start = sys._is_gil_enabled()  # type: ignore[attr-defined,unused-ignore]
 
 
 def pytest_report_header(config: pytest.Config) -> str:
@@ -28,7 +28,7 @@ def pytest_terminal_summary(terminalreporter: pytest.TerminalReporter) -> None:
     if (
         FREE_THREADED_BUILD
         and not gil_enabled_at_start
-        and sys._is_gil_enabled()  # type: ignore[attr-defined]
+        and sys._is_gil_enabled()  # type: ignore[attr-defined,unused-ignore]
     ):
         tr = terminalreporter
         tr.ensure_newline()

pyproject.toml

@@ -187,7 +187,6 @@ lint.isort.required-imports = [
 max_supported_python = "3.15"
 
 [tool.mypy]
-python_version = "3.11"
 disallow_subclassing_any = false
 disallow_untyped_calls = false
 warn_return_any = false

src/PIL/GifImagePlugin.py

@@ -1195,8 +1195,9 @@ class Collector(BytesIO):
         data = []
 
         def write(self, data: Buffer) -> int:
-            self.data.append(data)
-            return len(data)
+            data_bytes = bytes(data)
+            self.data.append(data_bytes)
+            return len(data_bytes)
 
     im.load()  # make sure raster data is available