gh-151596: Add missing argument 'size' to pure-Python implementation of TextIOBase.readline (GH-151679)

(cherry picked from commit 30aeeb3)

Co-authored-by: saber-bit <bryanventura0324@gmail.com>

Author: Saber0324

Lib/_pyio.py

@@ -1856,7 +1856,7 @@ def truncate(self, pos=None):
         """Truncate size to pos, where pos is an int."""
         self._unsupported("truncate")
 
-    def readline(self):
+    def readline(self, size=-1, /):
         """Read until newline or EOF.
 
         Returns an empty string if EOF is hit immediately.

Misc/NEWS.d/next/Library/2026-06-18-23-59-46.gh-issue-151596.5ma144.rst

@@ -0,0 +1 @@
+Add missing ``size`` positional argument to the pure-Python implementation of :meth:`io.TextIOBase.readline`.