Perform index checking in a caller thread (elastic#82249)

Since 8.11 lucene performs index checking concurrently
using disposable fixed thread pool executor by default.
Setting thread count to 1 to keep prior behavior
(check is executed in single caller thread).

server/src/main/java/org/elasticsearch/index/store/Store.java

@@ -340,6 +340,9 @@ public void renameTempFilesSafe(Map<String, String> tempFileMap) throws IOExcept
     public CheckIndex.Status checkIndex(PrintStream out) throws IOException {
         metadataLock.writeLock().lock();
         try (CheckIndex checkIndex = new CheckIndex(directory)) {
+            // Since 8.11 lucene performs index checking concurrently using disposable fixed thread pool executor by default.
+            // Setting thread count to 1 to keep prior behaviour (check is executed in single caller thread).
+            checkIndex.setThreadCount(1);
             checkIndex.setInfoStream(out);
             return checkIndex.checkIndex();
         } finally {

x-pack/plugin/searchable-snapshots/src/internalClusterTest/java/org/elasticsearch/xpack/searchablesnapshots/FrozenSearchableSnapshotsIntegTests.java

@@ -81,7 +81,6 @@
 
 public class FrozenSearchableSnapshotsIntegTests extends BaseFrozenSearchableSnapshotsIntegTestCase {
 
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/81949")
     public void testCreateAndRestorePartialSearchableSnapshot() throws Exception {
         final String fsRepoName = randomAlphaOfLength(10);
         final String indexName = randomAlphaOfLength(10).toLowerCase(Locale.ROOT);

x-pack/plugin/searchable-snapshots/src/main/java/org/elasticsearch/xpack/searchablesnapshots/store/input/BaseSearchableSnapshotIndexInput.java

@@ -301,7 +301,6 @@ protected final boolean assertCurrentThreadMayAccessBlobStore() {
             || threadName.contains('[' + SearchableSnapshots.CACHE_PREWARMING_THREAD_POOL_NAME + ']')
 
             // Unit tests access the blob store on the main test thread; simplest just to permit this rather than have them override this
-            // method somehow.
             || threadName.startsWith("TEST-")
             || threadName.startsWith("LuceneTestCase") : "current thread [" + Thread.currentThread() + "] may not read " + fileInfo;
         return true;