The current request header change detection doesn't work well with subrequest

[spacewander]

The current change detection only marks the current request, but not the main request if the current request is subrequest:

apisix-nginx-module/src/ngx_http_apisix_module.c

Line 565 in 1af1ee4

ngx_http_apisix_mark_request_header_set(ngx_http_request_t *r)

However, the headers_in field is shared between subrequest and the main request.