Add more nullability annotations to module/spring-boot-flyway

See gh-46587

Author: mhalbritter

module/spring-boot-flyway/src/main/java/org/springframework/boot/flyway/docker/compose/JdbcAdaptingFlywayConnectionDetailsFactory.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.flyway.docker.compose;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.autoconfigure.service.connection.ConnectionDetailsFactory;
 import org.springframework.boot.flyway.autoconfigure.FlywayConnectionDetails;
 import org.springframework.boot.jdbc.autoconfigure.JdbcConnectionDetails;
@@ -34,12 +36,12 @@ public FlywayConnectionDetails getConnectionDetails(JdbcConnectionDetails input)
 		return new FlywayConnectionDetails() {
 
 			@Override
-			public String getUsername() {
+			public @Nullable String getUsername() {
 				return input.getUsername();
 			}
 
 			@Override
-			public String getPassword() {
+			public @Nullable String getPassword() {
 				return input.getPassword();
 			}