[3.8] bpo-41841: prepare for 3.8.9 (GH-24635)

[3.8] bpo-41841: prepare for 3.8.9 (GH-24635) · python/cpython@653e17b

Original file line number	Diff line number	Diff line change
`@@ -1,12 +1,16 @@`
`1`		`-What's New in IDLE 3.8.8`
`2`		`-Released on 2021-02-15?`
`3`		`-======================================`
	`1`	`+What's New in IDLE 3.8.9`
	`2`	`+Released on 2021-05-03?`
	`3`	`+=========================`
`4`	`4`
`5`	`5`
`6`	`6`	`bpo-43283: Document why printing to IDLE's Shell is often slower than`
`7`	`7`	`printing to a system terminal and that it can be made faster by`
`8`	`8`	`pre-formatting a single string before printing.`
`9`	`9`
	`10`	`+What's New in IDLE 3.8.8`
	`11`	`+Released on 2021-02-19`
	`12`	`+======================================`
	`13`	`+`
`10`	`14`	`bpo-23544: Disable Debug=>Stack Viewer when user code is running or`
`11`	`15`	`Debugger is active, to prevent hang or crash. Patch by Zackery Spytz.`
`12`	`16`