Pending RELEASE-NOTES for the upcoming release

This is work in progress and will change before the release goes public on 22nd of September 2021.

Changes:

Bugfixes:

• Curl_http2_setup: don't change connection data on repeat invokes
• curl_multi_fdset: make FD_SET() not operate on sockets out of range
• dist: provide lib/.checksrc in the tarball
• FAQ: add GOPHERS + curl works on data, not files
• hsts: CURLSTS_FAIL from hsts read callback should fail transfer
• hsts: handle unlimited expiry
• http: fix the broken >3 digit response code detection
• strerror: use sys_errlist instead of strerror on Windows
• test1184: disable
• tests/sshserver.pl: make it work with openssh-8.7p1

Contributors:

0xee on github, Daniel Stenberg, Evangelos Foutras, Glenn de boer, Jonathan Cardoso Machado, Kamil Dudka, Marcel Raad, Ray Satiro, RiderALT on github, tawmoto on github, Viktor Szakats,