Fix product dependency for RxRelay

[via-guy]

In my project I have the following in my Package.swift

    dependencies: [
        .package(url: "https://github.com/ReactiveX/RxSwift.git", "6.0.0"..<"7.0.0"),
        .package(url: "https://github.com/CombineCommunity/RxCombine.git", "2.0.0"..<"3.0.0")
    ],
    targets: [
        .target(
            name: "MyProject",
            dependencies: [
                "RxSwift",
                .product(name: "RxCocoa", package: "RxSwift"),
                "RxCombine",
            ]
        ),

This throws the error

product 'RxRelay' required by package 'rxcombine' target 'RxCombine' not found.

My change fixes that.