ftp.funet.fi is misconfigured and handles content-encoding incorrectly

ftp.funet.fi seems to be badly misconfigured as it unconditionally serves .gz files as

Content-Type: application/xml
Content-Encoding: x-gzip

even if accept-encoding headers is not passed. This leads to client failures as in this case HTTP library transparently decompressed the content, while client code still expecting compressed content.

% curl -I https://ftp.funet.fi/pub/mirrors/ftp.opensuse.com/pub/opensuse/update/leap/15.6/oss/repodata/2cd535dd8479340ddfb645a33e939dc7431947006524bd6f79fcacc04dbe5b1f-primary.xml.gz
HTTP/1.1 200 OK
Date: Wed, 20 May 2026 14:51:23 GMT
Server: Apache/2.4.67 (Unix) OpenSSL/3.5.5
Last-Modified: Mon, 18 May 2026 10:34:18 GMT
ETag: "b0054-652151ad5dcbb"
Accept-Ranges: bytes
Content-Length: 720980
Content-Type: application/xml
Content-Encoding: x-gzip

Here are responses from correctly behaving mirrors:

% curl -I https://opensuse.koyanet.lv/update/leap/15.6/oss/repodata/2cd535dd8479340ddfb645a33e939dc7431947006524bd6f79fcacc04dbe5b1f-primary.xml.gz 
HTTP/2 200 
server: nginx
date: Wed, 20 May 2026 14:52:46 GMT
content-type: application/gzip
content-length: 720980
last-modified: Mon, 18 May 2026 10:34:18 GMT
etag: "6a0aeb2a-b0054"
strict-transport-security: max-age=31536000; includeSubDomains
x-frame-options: DENY
x-content-type-options: nosniff
content-security-policy: frame-ancestors 'none'; upgrade-insecure-requests; base-uri 'none'; form-action 'none'; default-src 'none';
referrer-policy: no-referrer, strict-origin-when-cross-origin
accept-ranges: bytes

% curl -I https://mirror.aardsoft.fi/opensuse/update/leap/15.6/oss/repodata/2cd535dd8479340ddfb645a33e939dc7431947006524bd6f79fcacc04dbe5b1f-primary.xml.gz 
HTTP/2 200 
server: nginx/1.21.5
date: Wed, 20 May 2026 14:44:00 GMT
content-type: application/octet-stream
content-length: 720980
last-modified: Mon, 18 May 2026 10:34:18 GMT
etag: "6a0aeb2a-b0054"
accept-ranges: bytes

Reproduce the ftp.funet.fi response with the curl command and URL shown in the issue, then locate the MirrorCache code or configuration responsible for response headers. Verify behavior with and without an Accept-Encoding header; done means .gz responses no longer unconditionally advertise x-gzip and clients receive consistent content type and encoding headers.