chore: use Java 17 as compilation baseline (no 21 features in use)

Author: deki

samples/springboot3/graphql-pet-store/pom.xml

@@ -25,7 +25,7 @@
     </licenses>
 
     <properties>
-        <java.version>21</java.version>
+        <java.version>17</java.version>
     </properties>
 
     <dependencies>

samples/springboot3/pet-store-native/pom.xml

@@ -15,7 +15,7 @@
 	<name>pet-store-native</name>
 	<description>Sample of AWS with Spring Native</description>
 	<properties>
-		<java.version>21</java.version>
+		<java.version>17</java.version>
 		<spring-cloud.version>2022.0.5</spring-cloud.version>
 	</properties>
 	<dependencies>