Filtered query strings on proxy level appears in request

[EvgeniyGorbunenko]

Describe the bug
Filtered query strings on proxy level appears in request

To Reproduce
Steps to reproduce the behavior:
Configuration used:

{
    "$schema": "https://www.krakend.io/schema/v3.json",
    "version": 3,
    "name": "KrakenD Community API Gateway",
    "port": 80,
    "host": ["http://localhost:80"],
    "timeout": "3000ms",
    "debug_endpoint": true,
    "endpoints": [
        {
            "endpoint": "/test",
            "method": "GET",
            "backend": [
                {
                    "encoding": "json",
                    "method": "GET",
                    "host": ["http://localhost:80"],
                    "input_headers": ["test"],
                    "input_query_strings": ["test"],
                    "url_pattern": "/__debug/"
                }
            ],
            "input_headers": ["test", "test2"],
            "input_query_strings": ["test", "test2"]
        }
    ],
    "sequential_start": false
}

Steps to run the software:

1. KrakenD CE docker image/local build (go version go1.24.5 darwin/arm64 for example)
2. Run curl

curl --location 'http://localhost:80/test?test=test&test2=test2&test3=test3' \
--header 'test: test' \
--header 'test2: test2' \
--header 'test3: test3'

Expected behavior
Filtered query strings must not be present in request

Logs

2025/08/05 19:08:26 KRAKEND DEBUG: [ENDPOINT: /__debug/*] Method: GET
2025/08/05 19:08:26 KRAKEND DEBUG: [ENDPOINT: /__debug/*] URL: /__debug/?test=test&test2=test2
2025/08/05 19:08:26 KRAKEND DEBUG: [ENDPOINT: /__debug/*] Query: map[test:[test] test2:[test2]]
2025/08/05 19:08:26 KRAKEND DEBUG: [ENDPOINT: /__debug/*] Params: [{param /}]
2025/08/05 19:08:26 KRAKEND DEBUG: [ENDPOINT: /__debug/*] Headers: map[Accept-Encoding:[gzip] Test:[test] User-Agent:[Go-http-client/1.1]]
2025/08/05 19:08:26 KRAKEND DEBUG: [ENDPOINT: /__debug/*] Body: 
[GIN] 2025/08/05 - 19:08:26 | 200 |     157.584µs |             ::1 | GET      "/__debug/?test=test&test2=test2"
[GIN] 2025/08/05 - 19:08:26 | 200 |    2.657791ms |             ::1 | GET      "/test?test=test&test2=test2&test3=test3"

[EvgeniyGorbunenko]

PR with fix
#764

[github-actions]

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