Polish EnableConfigurationPropertiesImportSelector javadoc

Closes gh-15049

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/EnableConfigurationPropertiesImportSelector.java

@@ -39,7 +39,7 @@ import org.springframework.util.StringUtils;
  * {@link ConfigurationProperties} bean or not, depending on whether the enclosing
  * {@link EnableConfigurationProperties} explicitly declares one. If none is declared then
  * a bean post processor will still kick in for any beans annotated as external
- * configuration. If one is declared then it a bean definition is registered with id equal
+ * configuration. If one is declared, then a bean definition is registered with id equal
  * to the class name (thus an application context usually only contains one
  * {@link ConfigurationProperties} bean of each unique type).
  *