Fix tests

[joanhey]

First skip the tests that fail in all versions. So we can fix one by one.

And we see the tests, that fail only on some versions.

Fixed:

• [x] ngx_ini.t Remember that only pass variables using $ENV{'TEST_NGINX_xxxxx'} :stuck_out_tongue_closed_eyes:
• [x] ngx_header.t Fix double echo
• [x] ngx_socket.t Now use httpbin.org (hq.sinajs.cn return always Forbidden)

Ngx_mysql async test fail, only in this repo #152. @rryqszq4 this one is for you. And fix the var_dump() in PHP >=7.4

Ready to be merged.

[joanhey]

I will try to add more tests in other PRs.