[MINOR] Fix run-scala-test.sh to always use build/mvn for JVM args extraction (apache#11598)

mvnd returns empty output for help:evaluate goal, causing --add-opens
JVM flags to be missing. This broke Arrow memory initialization in tests
like GlutenParquetTypeWideningSuite.

Author: baibaichen

dev/run-scala-test.sh

@@ -557,7 +557,8 @@ log_step "Step 2: Getting JVM arguments from pom.xml..."
 
 TIMER_STEP2_START=$(timer_now)
 
-JVM_ARGS_RAW=$(${MVN_CMD} help:evaluate \
+# Always use build/mvn for help:evaluate (mvnd returns empty output for this goal)
+JVM_ARGS_RAW=$(./build/mvn help:evaluate \
   -Dexpression=extraJavaTestArgs \
   -q -DforceStdout \
   -P"${PROFILES}" 2>/dev/null || echo "")