gh-143201: warnings writes the full source line instead of the truncated one

The truncated object is meant to be written instead.

Author: AZero13

Misc/NEWS.d/next/Core_and_Builtins/2025-12-26-17-18-18.gh-issue-143201.UbXuX4.rst

@@ -0,0 +1 @@
+Print out the truncated line, not the raw sourceline.

Python/_warnings.c

@@ -697,7 +697,7 @@ show_warning(PyThreadState *tstate, PyObject *filename, int lineno,
         if (truncated == NULL)
             goto error;
 
-        PyFile_WriteObject(sourceline, f_stderr, Py_PRINT_RAW);
+        PyFile_WriteObject(truncated, f_stderr, Py_PRINT_RAW);
         Py_DECREF(truncated);
         PyFile_WriteString("\n", f_stderr);
     }