Fix assertion in SnapshotShutdownIT.testSnapshotShutdownProgressTracker() (#127998)

Relaxes a log expectation assertion from an exact test
of numShards running snapshots to 1-numShards, since it
is possible for some of the shard snapshot statuses to
already be in stage=PAUSED.

Closes #127690

Author: JeremyDahlgren

muted-tests.yml

@@ -417,9 +417,6 @@ tests:
 - class: org.elasticsearch.action.admin.indices.diskusage.IndexDiskUsageAnalyzerTests
   method: testKnnVectors
   issue: https://github.com/elastic/elasticsearch/issues/127689
-- class: org.elasticsearch.snapshots.SnapshotShutdownIT
-  method: testSnapshotShutdownProgressTracker
-  issue: https://github.com/elastic/elasticsearch/issues/127690
 - class: org.elasticsearch.backwards.MixedClusterClientYamlTestSuiteIT
   method: test {p0=search/350_point_in_time/point-in-time with index filter}
   issue: https://github.com/elastic/elasticsearch/issues/127741

server/src/internalClusterTest/java/org/elasticsearch/snapshots/SnapshotShutdownIT.java

@@ -480,7 +480,7 @@ public void testShutdownWhileSuccessInFlight() throws Exception {
     )
     public void testSnapshotShutdownProgressTracker() throws Exception {
         final var repoName = randomIdentifier();
-        final int numShards = randomIntBetween(1, 10);
+        final int numShards = randomIntBetween(1, 9);
         createRepository(repoName, "mock");
 
         // Create another index on another node which will be blocked (remain in state INIT) throughout.
@@ -540,12 +540,14 @@ public void testSnapshotShutdownProgressTracker() throws Exception {
         mockLog.awaitAllExpectationsMatched();
         resetMockLog();
 
+        // At least one shard reached the MockRepository's blocking code when waitForBlock was called. However, there's no guarantee that
+        // the other shards got that far before the shutdown flag was put in place, in which case the other shards may be paused instead.
         mockLog.addExpectation(
-            new MockLog.SeenEventExpectation(
+            new MockLog.PatternSeenEventExpectation(
                 "SnapshotShutdownProgressTracker running number of snapshots",
                 SnapshotShutdownProgressTracker.class.getCanonicalName(),
                 Level.INFO,
-                "*Number shard snapshots running [" + numShards + "].*"
+                ".+Number shard snapshots running \\[[1-" + numShards + "]].+"
             )
         );