Update Iceberg to 1.8.1

Author: ebyhr

testing/spark3-iceberg/Dockerfile

@@ -15,7 +15,7 @@ FROM testing/almalinux9-oj11:unlabelled$ARCH
 
 ARG SPARK_VERSION=3.4.2
 ARG HADOOP_VERSION=3
-ARG ICEBERG_VERSION=1.7.0
+ARG ICEBERG_VERSION=1.8.1
 # ICEBERG_JAR_VERSION is derived from: <spark-version>_<scala-version>
 ARG ICEBERG_JAR_VERSION=3.4_2.12
 ARG POSTGRESQL_JAR_VERSION=42.3.5