Increase max heap of the Maven JVM

The overhead of build scans seems to have brought us right to the limit
of the Maven JVM's heap. As a result, builds are occasionally failing
as the heap's been exhausted.

This commit increases the JVM's max heap.

Closes gh-22649

.mvn/jvm.config

@@ -1 +1 @@
--Xmx1536m
+-Xmx2048m