testing/althttpd: upgrade to 202102112256
Cumulative update. Upstream commit comments:
- MegaIndex.ru is aggressive and bypasses Javascript attempts to keep out robots. It accounts for a large percentage of the traffice at sqlite.org, but provides no benefit. So exclude it.
- A new robot restriction.
- Remove unreachable code from the RFC822 date parser.
- Fix a typo in a comment.
- On the RFC5322 date-time string, use GMT rather than +0000.