[Y-Build] Use latest Y-build repository as baseline for comparison.

TODO: address
eclipse-platform#2625 (comment)

Fixes eclipse-platform#2793

eclipse-platform-parent/pom.xml

@@ -816,6 +816,20 @@
         </repository>
       </repositories>
     </profile>
+    <profile>
+      <id>jdt-y-build</id>
+      <activation>
+        <property>
+          <name>env.BUILD_TYPE</name>
+          <value>Y</value>
+        </property>
+      </activation>
+      <properties>
+        <latest-Y-build-repo>https://download.eclipse.org/eclipse/updates/${releaseVersion}-Y-builds</latest-Y-build-repo>
+        <!-- Use latest Y-build instead of I-build repo as baseline for Y-builds -->
+        <comparator.repo>${latest-Y-build-repo}</comparator.repo>
+      </properties>
+    </profile>
     <profile>
       <id>eclipse-sign</id>
       <build>