Conform ServiceGroup to Service

# Motivation

It is possible to nest a `ServiceGroup` inside another `ServiceGroup` however we were missing the conformance to `Service` on the group.

# Modification

This PR adds the conformance to `Service` to `ServiceGroup`.

Author: FranzBusch

Sources/ServiceLifecycle/ServiceGroup.swift

@@ -16,7 +16,7 @@ import Logging
 import UnixSignals
 
 /// A ``ServiceGroup`` is responsible for running a number of services, setting up signal handling and signalling graceful shutdown to the services.
-public actor ServiceGroup: Sendable {
+public actor ServiceGroup: Sendable, Service {
     /// The internal state of the ``ServiceGroup``.
     private enum State {
         /// The initial state of the group.
@@ -104,6 +104,16 @@ public actor ServiceGroup: Sendable {
         self.maximumCancellationDuration = configuration._maximumCancellationDuration
     }
 
+    /// Runs all the services by spinning up a child task per service.
+    /// Furthermore, this method sets up the correct signal handlers
+    /// for graceful shutdown.
+    // We normally don't use underscored attributes but we really want to use the method with
+    // file and line whenever possible.
+    @_disfavoredOverload
+    public func run() async throws {
+        try await self.run(file: #file, line: #line)
+    }
+
     /// Runs all the services by spinning up a child task per service.
     /// Furthermore, this method sets up the correct signal handlers
     /// for graceful shutdown.