test(spanner): restrict pagination test to explicitly created database (#14043)

The `ITBackupTest.testPagination` method previously listed all backups
on the instance and asserted that only a single page of results would be
returned (`assertFalse(page.hasNextPage())`). When running on shared
integration test instances (`spanner.testenv.instance`), this assertion
would fail if backups from other test runs were present on the instance.

This commit updates the pagination API calls to use
`Options.filter("database:" + databaseId)`, ensuring that the test only
paginates over the backups associated with the uniquely generated
database for the active test run. This prevents the test from failing
due to unrelated backups in the shared test environment.

Author: sakthivelmanii

java-spanner/google-cloud-spanner/src/test/java/com/google/cloud/spanner/it/slow/ITBackupTest.java

@@ -358,7 +358,7 @@ public void test01_Backups() throws InterruptedException, ExecutionException, Ti
             backup));
 
     // Test pagination.
-    testPagination();
+    testPagination(database);
     logger.info("Finished listBackup tests");
 
     // Execute other tests as part of this integration test to reduce total execution time.
@@ -705,20 +705,21 @@ private void testUpdateBackup(Backup backup) {
     assertEquals(tomorrow, backup.getExpireTime());
   }
 
-  private void testPagination() {
+  private void testPagination(Database database) {
     logger.info("Listing backups using pagination");
+    Options.ListOption filter =
+        Options.filter(String.format("database:%s", database.getId().getName()));
 
     // First get all current backups without using pagination so we can compare that list with
     // the same list when pagination fails.
     List<Backup> initialBackups =
-        Lists.newArrayList(dbAdminClient.listBackups(instanceId).iterateAll());
+        Lists.newArrayList(dbAdminClient.listBackups(instanceId, filter).iterateAll());
 
     int numBackups = 0;
     logger.info("Fetching first page");
-    Page<Backup> page = dbAdminClient.listBackups(instanceId, Options.pageSize(1));
+    Page<Backup> page = dbAdminClient.listBackups(instanceId, filter, Options.pageSize(1));
     assertEquals(1, Iterables.size(page.getValues()));
     numBackups++;
-    assertFalse(page.hasNextPage());
     Set<String> seenPageTokens = new HashSet<>();
     seenPageTokens.add("");
     while (page.hasNextPage()) {
@@ -745,11 +746,11 @@ private void testPagination() {
       seenPageTokens.add(page.getNextPageToken());
       page =
           dbAdminClient.listBackups(
-              instanceId, Options.pageToken(page.getNextPageToken()), Options.pageSize(1));
+              instanceId, filter, Options.pageToken(page.getNextPageToken()), Options.pageSize(1));
       assertEquals(1, Iterables.size(page.getValues()));
       numBackups++;
     }
-    assertTrue(numBackups >= 1);
+    assertEquals(initialBackups.size(), numBackups);
   }
 
   private void testRestore(Backup backup, Timestamp versionTime, String expectedKey)