Bump dependency versions (#38)

IntegrationTests/PluginTests/Resources/Package.swift

@@ -31,7 +31,7 @@ let package = Package(
 
     .package(
       url: "https://github.com/grpc/grpc-swift.git",
-      branch: "main"
+      exact: "2.0.0-rc.1"
     )
   ],
   targets: [

Package.swift

@@ -35,7 +35,7 @@ let products: [Product] = [
 let dependencies: [Package.Dependency] = [
   .package(
     url: "https://github.com/grpc/grpc-swift.git",
-    branch: "main"
+    exact: "2.0.0-rc.1"
   ),
   .package(
     url: "https://github.com/apple/swift-protobuf.git",