Fix broken link in PR checklist (qmk#23877)

docs/pr_checklist.md

@@ -88,7 +88,7 @@ https://github.com/qmk/qmk_firmware/pulls?q=is%3Apr+is%3Aclosed+label%3Akeyboard
  - RGB Matrix Configuration
  - Run `qmk format-json` on this file before submitting your PR. Be sure to append the `-i` flag to directly modify the file, or paste the outputted code into the file. 
 - `readme.md`
- - must follow the [template](https://github.com/qmk/qmk_firmware/blob/master/data/templates/keyboard/readme)
+ - must follow the [template](https://github.com/qmk/qmk_firmware/blob/master/data/templates/keyboard/readme.md)
  - flash command is present, and has `:flash` at end
  - valid hardware availability link (unless handwired) -- private groupbuys are okay, but one-off prototypes will be questioned. If open-source, a link to files should be provided.
  - clear instructions on how to reset the board into bootloader mode