Try Maven Central before hitting repository.apache.org

We have noticed some builds causing many 404 errors on
`repository.apache.org`, causing GitHub Actions runners
to be banned (https://infra.apache.org/infra-ban.html).

Looking at various logs, it looks like this workflow
may be one of the jobs triggering this problem. Including
Maven Central explicitly in the repositories section will
make Maven check that repository first, which should help
a lot.

.ci/jenkins/tests/pom.xml

@@ -27,6 +27,14 @@
     <packaging>jar</packaging>
 
     <repositories>
+        <repository>
+            <snapshots>
+                <enabled>false</enabled>
+            </snapshots>
+            <id>central</id>
+            <name>Central Repository</name>
+            <url>https://repo.maven.apache.org/maven2</url>
+        </repository>
         <repository>
             <id>apache-public-repository-group</id>
             <name>Apache Public Repository Group</name>