Duplicate date http headers for some resources

Describe the bug
For some files, duplicate Date header is sent

Version
v0.55.8

How did you install?

LXC from proxmox scripts

Steps to reproduce the behavior:
curl -v -s http://1.2.3.5:5000/static/js/jquery-3.6.0.min.js 1> /dev/null:

*   Trying 1.2.3.5:5000...
* Connected to 1.2.3.5 (1.2.3.5) port 5000
* using HTTP/1.x
> GET /static/js/jquery-3.6.0.min.js HTTP/1.1
> Host: 1.2.3.5:5000
> User-Agent: curl/8.14.1
> Accept: */*
>
* Request completely sent off
< HTTP/1.1 200 OK
< Server: Werkzeug/3.1.6 Python/3.13.14
< Date: Tue, 04 Aug 2026 12:04:07 GMT
< Content-Disposition: inline; filename=jquery-3.6.0.min.js
< Content-Type: text/javascript; charset=utf-8
< Content-Length: 89501
< Last-Modified: Wed, 29 Jul 2026 22:57:56 GMT
< Cache-Control: no-cache, max-age=0
< Expires: Tue, 04 Aug 2026 12:04:07 GMT
< ETag: "1785365876.4483783-89501-3283166620"
< Date: Tue, 04 Aug 2026 12:04:07 GMT
< Access-Control-Allow-Origin: *
< Vary: Cookie
< Connection: close
<
{ [10928 bytes data]
* shutting down connection #0

Expected behavior
Single header should be sent

Additional context
NGINX Warn:
[warn] 3279#3279: *150 upstream sent duplicate header line: "Date: Tue, 04 Aug 2026 11:55:09 GMT", previous value: "Date: Tue, 04 Aug 2026 11:55:09 GMT", ignored while reading response header from upstream, client: 1.2.3.4, server: example.com, request: "GET /static/js/jquery-3.6.0.min.js HTTP/3.0", upstream: "http://1.2.3.5:5000/static/js/jquery-3.6.0.min.js", referrer: "https://example.com/"

the same (similar?) issue https://github.com/dgtlmoon/changedetection.io/issues/4101

Analysis with potential solution by AI: https://github.com/dgtlmoon/changedetection.io/issues/4101#issuecomment-5178904903