To formalize they are now XML-compliant (with some asterisks.)
Also to help syntax highlighters work on them to make their content more
readable.
Also:
- Delete empty comment decorations.
- GHA/checksrc: simplify XML check.
- runtests: fail to load test data with XML prolog missing.
Follow-up to bfe6eb1c06#19927
Follow-up to 87ba80a6dfCloses#19946
Test-case 1515 reproduces bug #1303, where libcurl
would incorrectly prune DNS entries added via
CURLOPT_RESOLVE after the DNS_CACHE_TIMEOUT had
expired.