Adapt to improvements in Nullaway 0.13.8

This commit adapts @Nullable when calling Map#remove as it correctly
handles nullability.

See gh-50972

Signed-off-by: Manu Sridharan <msridhar@gmail.com>

module/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/RestartScopeInitializer.java

@@ -47,7 +47,7 @@ public class RestartScopeInitializer implements ApplicationContextInitializer<Co
 		}
 
 		@Override
-		public Object remove(String name) {
+		public @Nullable Object remove(String name) {
 			return Restarter.getInstance().removeAttribute(name);
 		}
 

module/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/Restarter.java

@@ -450,7 +450,7 @@ public class Restarter {
 		return value;
 	}
 
-	public Object removeAttribute(String name) {
+	public @Nullable Object removeAttribute(String name) {
 		return this.attributes.remove(name);
 	}