Fix notbefore

[osirisinferi]

The CSV file and this page mention(ed) that the date in the CSV file is the notBefore date of a certificate. However, it is the notAfter datetime.

This is already fixed in the CSV, but as mentioned on the Community this page is still mentioning the date as notBefore (but in other words).

This PR corrects the above.

This PR also changes back the date variable of the page to the date the page was originally written, which was simultaneously updated with the lastmod date in #1383 which probably shouldn't have. Correct me if I'm wrong, but my gut says the date value is the date on which the page was originally written and the lastmod value is the one which needs to be updated with every update. And not date.