Port the multi connection fixes from #24 to the older nginx patches #25

#24 fixed these in nginx-1.31.8.patch, the patch apisix-runtime ships. The older nginx-*.patch files (1.19.3 to 1.31.1) still have the old code in the patched ngx_http_upstream_connect():

1. A new connection that connects immediately (e.g. a unix socket upstream) is taken for a reused one and the request fails with 500.
2. A request that lands on a reused connection that is still connecting fails with 500 instead of waiting for the connect.
3. All three error branches log through c->log after finalizing, and finalizing can free the pool that owns it.

The fix for each is the ngx_http_upstream_connect() hunk of nginx-1.31.8.patch from #24. The pc->cached = 0 change in ngx_http_multi_upstream_get_peer() that it relies on is in the module source, so it already applies to every version.

These only matter for builds that combine an older OpenResty with a module release that includes #24. api7ee-runtime pins 1.1.1.