[test] Spark 4.x Test should not use multiple process

Author: JingsongLi

.github/workflows/utitcase-spark-4.x.yml

@@ -58,6 +58,6 @@ jobs:
           test_modules+="org.apache.paimon:paimon-spark-${suffix},"
           done
           test_modules="${test_modules%,}"
-          mvn -T 2C -B test -pl "${test_modules}" -Duser.timezone=$jvm_timezone -Pspark4
+          mvn -T 1C -B test -pl "${test_modules}" -Duser.timezone=$jvm_timezone -Pspark4
         env:
           MAVEN_OPTS: -Xmx4096m