Revert poem sample's dependency

Author: jmartisk

samples/email-a-poem/pom.xml

@@ -18,7 +18,7 @@
         <quarkus.platform.version>3.15.1</quarkus.platform.version>
         <skipITs>true</skipITs>
         <surefire-plugin.version>3.2.5</surefire-plugin.version>
-        <quarkus-langchain4j.version>999-SNAPSHOT</quarkus-langchain4j.version>
+        <quarkus-langchain4j.version>0.21.0.CR1</quarkus-langchain4j.version>
     </properties>
 
     <dependencyManagement>