Allow for custom stacklevel in deprecations

Author: radarhere

src/PIL/PngImagePlugin.py

@@ -1370,7 +1370,7 @@ def _save(
         msg = f"cannot write mode {mode} as PNG"
         raise OSError(msg) from e
     if outmode == "I":
-        deprecate("Saving I mode images as PNG", 13)
+        deprecate("Saving I mode images as PNG", 13, stacklevel=4)
 
     #
     # write minimal PNG file

src/PIL/_deprecate.py

@@ -12,6 +12,7 @@ def deprecate(
     *,
     action: str | None = None,
     plural: bool = False,
+    stacklevel: int = 3,
 ) -> None:
     """
     Deprecations helper.
@@ -67,5 +68,5 @@ def deprecate(
     warnings.warn(
         f"{deprecated} {is_} deprecated and will be removed in {removed}{action}",
         DeprecationWarning,
-        stacklevel=3,
+        stacklevel=stacklevel,
     )