WEB: fix discussion link in PDEP-6

Author: jorisvandenbossche

web/pandas/pdeps/0006-ban-upcasting.md

@@ -2,7 +2,7 @@
 
 - Created: 23 December 2022
 - Status: Implemented
-- Discussion: [#39584](https://github.com/pandas-dev/pandas/pull/50402)
+- Discussion: [#50424](https://github.com/pandas-dev/pandas/pull/50424)
 - Author: [Marco Gorelli](https://github.com/MarcoGorelli) ([original issue](https://github.com/pandas-dev/pandas/issues/39584) by [Joris Van den Bossche](https://github.com/jorisvandenbossche))
 - Revision: 1