[SPARK-48946][SQL] NPE in redact method when session is null

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

If we call DataSourceV2ScanExecBase redact method from a thread that don't have a session in thread local we get an NPE. Getting stringRedactionPattern from conf could prevent this problem as conf checks if session is null or not. We also use this in DataSourceScanExec trait.
https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/DataSourceScanExec.scala#L93-L95

### Why are the changes needed?

To prevent NPE when session is null.

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

No

### How was this patch tested?

Existing UTs.

### Was this patch authored or co-authored using generative AI tooling?

No

Closes apache#47419 from mikoszilard/SPARK-48946.

Authored-by: Szilard Miko <smiko@cloudera.com>
Signed-off-by: Dongjoon Hyun <dhyun@apple.com>

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/DataSourceV2ScanExecBase.scala

@@ -71,7 +71,7 @@ trait DataSourceV2ScanExecBase extends LeafExecNode {
    * Shorthand for calling redact() without specifying redacting rules
    */
   protected def redact(text: String): String = {
-    Utils.redact(session.sessionState.conf.stringRedactionPattern, text)
+    Utils.redact(conf.stringRedactionPattern, text)
   }
 
   override def verboseStringWithOperatorId(): String = {