Gradle deprecation warnings: replace Groovy DSL property assignment syntax

While building Iceberg with recent Gradle versions, I see deprecation warnings:

"Properties should be assigned using the 'propName = value' syntax..."

This occurs due to usage of deprecated Groovy DSL syntax like:
exceptionFormat 'full'

Suggested fix:
Replace with:
exceptionFormat = 'full'

This will be required for Gradle 10 compatibility.