repo-sql-impl: added postgresql, dep analyzer is lying, but that's OK

The dep comes transitively from repo-sqlbase anyway, so it's technically
there, but it's not mentioned in the code at all. Bad plugin boy.

repo/repo-sql-impl/pom.xml

@@ -141,6 +141,11 @@
             <groupId>com.h2database</groupId>
             <artifactId>h2</artifactId>
         </dependency>
+        <!-- This is not used here directly, but dep plugin is complaining, argh... -->
+        <dependency>
+            <groupId>org.postgresql</groupId>
+            <artifactId>postgresql</artifactId>
+        </dependency>
 
         <dependency>
             <groupId>com.querydsl</groupId>