Fix Renovate config

[hugovk]

Fixes #6598

Changes proposed in this pull request:

• Follow on from Configure Renovate #6564 (comment)
• It can't parse "on the third day of the month"
• Let's try "on the 3rd day of the month"

[hugovk]

Looks like Renovate uses Later.js for parsing the schedule:

renovatebot/renovate#11098 (comment)

This online tester suggests it doesn't like "on the third day of the month" but "on the 3rd day of the month" should be fine:

https://codepen.io/antonlydike/full/Kgygpr

[hugovk]

Same thing parse error was happening in python-pillow/pillow-wheels#321 with "on the fourth day of the month" but it's now happy with "on the 4th day of the month" 👍

Similarly in python-pillow/docker-images#156 with "fifth" -> "5th".