Change the hardcoded Drupal version in core.

re-roll 10.x.dev branch.

Patch #13 applied cleanly on 10.1.x-dev.

Patch #13 applied successfully and it's working as expected.

As suggested in #6 and #8 I think we should remove the version number entirely and just say "Drupal PHP requirements handbook page".

made changes according to #16

Oh, I didn't spot that this change has already been made in #3261611: Fix PHP requirements link and standardize the strings that reference it → - closing as a duplicate of that issue.