Use https instead of SSH for Swift-Protobuf dependency

Author: jbackertm

Package.swift

@@ -35,7 +35,7 @@ let package = Package(
     ],
     dependencies: [
         // Dependencies declare other packages that this package depends on.
-        .package(url: "git@github.com:apple/swift-protobuf.git", exact: "1.28.2"),
+        .package(url: "https://github.com/apple/swift-protobuf.git", exact: "1.28.2"),
     ],
     targets: [
         // Targets are the basic building blocks of a package. A target can define a module or a test suite.