change default Maven profile to Spark 4.0

#4140 changed the default profile to Spark 4.1, but I think that was premature considering we don't have Iceberg support on 4.1 yet. Iceberg 1.11 only released last week with Spark 4.1 support, and #4381 tracks Comet supporting Iceberg 1.11.

In the meantime, I manually set my environment to 4.0 locally for development, and would prefer others do the same to hopefully avoid breaking Iceberg compatibility accidentally.