Upgrade mypy to 1.15

Makefile

@@ -28,7 +28,7 @@ fate-suite:
 	rsync -vrltLW rsync://fate-suite.ffmpeg.org/fate-suite/ tests/assets/fate-suite/
 
 lint:
-	$(PIP) install -U black isort flake8 flake8-pyproject pillow numpy mypy==1.13.0 pytest
+	$(PIP) install -U black isort flake8 flake8-pyproject pillow numpy mypy==1.15.0 pytest
 	black --check av examples tests setup.py
 	flake8 av
 	isort --check-only --diff av examples tests

av/error.pyi

@@ -8,8 +8,8 @@ def tag_to_code(tag: bytes) -> int: ...
 def err_check(res: int, filename: str | None = None) -> int: ...
 
 class FFmpegError(Exception):
-    errno: int
-    strerror: str
+    errno: int | None
+    strerror: str | None
     filename: str
     log: tuple[int, tuple[int, str, str] | None]
 

av/error.pyx

@@ -95,11 +95,13 @@ class FFmpegError(Exception):
             pass
 
     def __str__(self):
-        msg = f"[Errno {self.errno}] {self.strerror}"
-
+        msg = ""
+        if self.errno is not None:
+            msg = f"{msg}[Errno {self.errno}] "
+        if self.strerror is not None:
+            msg = f"{msg}{self.strerror}"
         if self.filename:
             msg = f"{msg}: {self.filename!r}"
-
         if self.log:
             msg = f"{msg}; last error log: [{self.log[1].strip()}] {self.log[2].strip()}"