bpo-39943: Add the const qualifier to pointers on non-mutable PyUnicode data. (GH-19345)

Python/traceback.c

@@ -376,7 +376,7 @@ _Py_DisplaySourceLine(PyObject *f, PyObject *filename, int lineno, int indent)
     int fd;
     int i;
     char *found_encoding;
-    char *encoding;
+    const char *encoding;
     PyObject *io;
     PyObject *binary;
     PyObject *fob = NULL;
@@ -384,7 +384,7 @@ _Py_DisplaySourceLine(PyObject *f, PyObject *filename, int lineno, int indent)
     PyObject *res;
     char buf[MAXPATHLEN+1];
     int kind;
-    void *data;
+    const void *data;
 
     /* open the file */
     if (filename == NULL)