chore: fix the broken integration test

It looks like openjdk:8 is no longer available. (Fair, even Java 11 has
been out for 7 years now.)

Author: plumpy

integration/testdata/debug/java/pom.xml

@@ -22,7 +22,7 @@
         <version>${jib.maven-plugin-version}</version>
         <configuration>
           <from>
-            <image>openjdk:8</image> <!-- has jdb -->
+            <image>eclipse-temurin:25</image> <!-- has jdb -->
           </from>
           <container>
             <jvmFlags>