[SPARK-41183][SQL][FOLLOWUP] Change the name from injectPlanNormalizationRules to injectPlanNormalizationRule

### What changes were proposed in this pull request?

Followup of #38692. To follow other APIs in `SparkSessionExtensions`, the name should be `inject...Rule` and `build...Rules`.

### Why are the changes needed?

typo fix

### Does this PR introduce _any_ user-facing change?

not a released API

### How was this patch tested?

n/a

Closes #38767 from cloud-fan/small.

Authored-by: Wenchen Fan <wenchen@databricks.com>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>

Author: cloud-fan

sql/core/src/main/scala/org/apache/spark/sql/SparkSessionExtensions.scala

@@ -230,7 +230,7 @@ class SparkSessionExtensions {
    * cache hit rate by normalizing different plans to the same form. These rules should never modify
    * the result of the LogicalPlan.
    */
-  def injectPlanNormalizationRules(builder: RuleBuilder): Unit = {
+  def injectPlanNormalizationRule(builder: RuleBuilder): Unit = {
     planNormalizationRules += builder
   }
 

sql/core/src/test/scala/org/apache/spark/sql/SparkSessionExtensionSuite.scala

@@ -194,7 +194,7 @@ class SparkSessionExtensionSuite extends SparkFunSuite with SQLHelper {
 
   test("inject plan normalization rules") {
     val extensions = create { extensions =>
-      extensions.injectPlanNormalizationRules { session =>
+      extensions.injectPlanNormalizationRule { session =>
         org.apache.spark.sql.catalyst.optimizer.PushDownPredicates
       }
     }