fix: merge duplicate x-goog-request-params header

[cpriti-os]

This change fixes an issue where multiple x-goog-request-params headers were being sent on API requests, leading to "Invalid Bucket name errors". The headers are now correctly merged using an ampersand (&), similar to how x-goog-api-client handles multiple values.

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PR created automatically by Jules for task 4611007834348080142 started by @cpriti-os

[google-labs-jules]

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