Add back no-op setLoader to ServerProperties

Tomcat starts up with server.loader System property set so
we need to accept that.

[Fixes #50806851] [bs-141]
First class escape hatch from jar to war for web applications

spring-bootstrap/src/main/java/org/springframework/bootstrap/context/embedded/properties/ServerProperties.java

@@ -88,6 +88,10 @@ public class ServerProperties implements EmbeddedServletContainerCustomizer {
 		this.sessionTimeout = sessionTimeout;
 	}
 
+	public void setLoader(String value) {
+		// no op to support Tomcat running as a traditional container (not embedded)
+	}
+
 	@Override
 	public void customize(ConfigurableEmbeddedServletContainerFactory factory) {
 		factory.setPort(getPort());