Set the gradlew working dir more fully

For some reason, the CI attempts to run ./gradlew from
the directory target/gradle-scijava, rather than gradle-scijava.
Let's prepend the ${basedir} to be more explicit about what we want.

Author: ctrueden

pom.xml

@@ -6889,7 +6889,7 @@
 						</goals>
 						<configuration>
 							<executable>./gradlew</executable>
-							<workingDirectory>gradle-scijava</workingDirectory>
+							<workingDirectory>${basedir}/gradle-scijava</workingDirectory>
 							<arguments>
 								<argument>--project-cache-dir</argument>
 								<argument>../target/gradle/build</argument>