Cannot query label values if server.http_path_prefix is set

[moorglade]

Describe the bug
If I set server.http_path_prefix to any value, querying /<prefix>/loki/api/v1/label/<name>/values returns an error:

parse error : syntax error: unexpected $end

Other endpoints seem to work as expected.

To Reproduce

Steps to reproduce the behavior:

1. Set server.http_path_prefix in Loki configuration.
2. Started Loki 3.3.2.
3. Query /<prefix>/loki/api/v1/label/<name>/values API endpoint.

Expected behavior
The endpoint should return label values.

Environment:

• Infrastructure: bare-metal servers + Docker

Screenshots, Promtail config, or terminal output

curl --header "X-Scope-OrgID: test"  http://192.168.0.3:3100/my_prefix/loki/api/v1/label/filename/values?start=1735898264857000000
parse error : syntax error: unexpected $end

Possibly related to #2176