iceberg-rest-catalog: fix genrule

local = True was forcing local, unsandboxed execution and making the
build bypass the remote cache.

This commit:
- drops local = True so the action runs with a sandbox and can use
  remote cache,
- sets an explicit GRADLE_USER_HOME, otherwise would fallback on
  $HOME/.gradle which is read-only from the sandbox,
- drops the `chmod +x ./gradlew` which was unneeded, plus it breaks in
  the sandbox because it is read-only

Author: andrwng

tests/java/iceberg-rest-catalog/BUILD

@@ -14,11 +14,10 @@ genrule(
         OUT_PATH=$$(realpath $(OUTS))
         SRC_DIR=$$(dirname $(location gradlew))
         cd $$SRC_DIR
-        chmod +x ./gradlew
+        export GRADLE_USER_HOME="$$(pwd)/.gradle-home"
         ./gradlew --no-daemon shadowJar
         cp build/libs/iceberg-rest-catalog-all.jar $$OUT_PATH
     """,
-    local = True,
     tags = ["requires-network"],
     visibility = ["//visibility:public"],
 )