Tests - use nginx-http3:1.21.6 container

[macbre]

No description provided.

[macbre]

Failing tests caused by new set of response headers added after macbre/docker-nginx-http3#65

[macbre]

Expected value to deeply and strictly equal to:
      [{"size": 342, "url": "http://127.0.0.1:8888/static/blank.gif"}]
    Received:
      [{"size": 327, "url": "http://127.0.0.1:8888/static/blank.gif"}]

There's a difference of 15 bytes.

[macbre]

++ curl -svo /dev/null --compressed 0.0.0.0:8888/static/style.css
*   Trying 0.0.0.0:8888...
* TCP_NODELAY set
* Connected to 0.0.0.0 (127.0.0.1) port 8888 (#0)
> GET /static/style.css HTTP/1.1
> Host: 0.0.0.0:8888
> User-Agent: curl/7.68.0
> Accept: */*
> Accept-Encoding: deflate, gzip, br
> 
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Date: Tue, 26 Apr 2022 08:56:20 GMT
< Content-Type: text/css
< Content-Length: 22
< Last-Modified: Tue, 26 Apr 2022 08:[55](https://github.com/macbre/phantomas/runs/6172507199?check_suite_focus=true#step:6:55):[56](https://github.com/macbre/phantomas/runs/6172507199?check_suite_focus=true#step:6:56) GMT
< Connection: keep-alive
< ETag: "6267b39c-16"
< Expires: Wed, 27 Apr 2022 08:56:20 GMT
< Cache-Control: max-age=86400
< Accept-Ranges: bytes
< 
{ [22 bytes data]
* Connection #0 to host 0.0.0.0 left intact
* ```

[macbre]

< Server: nginx

is missing due to https://github.com/macbre/docker-nginx-http3/blob/master/nginx.conf#L36-L37

Exactly the missing 15 bytes!