Prevent AWS credentials refresh from stopping on exception

If `aws_credentials()` fails due to an unstable network or other issues,
it throws an exception. This stops `timer_execute()` from repeating its block,
preventing `OpenSearchOutput` from updating `@_aws_credentials`.
As a result, `@_aws_credentials` will expire.

This commit catches the exception and prevents it from propagating to
`timer_execute()`, ensuring continuous credential updates.

Signed-off-by: Yuki Sekiguchi <[email protected]>

lib/fluent/plugin/out_opensearch.rb

@@ -350,7 +350,11 @@ class << self
 
             @credential_mutex.synchronize do
               @_os = nil
-              @_aws_credentials = aws_credentials(@endpoint)
+              begin
+                @_aws_credentials = aws_credentials(@endpoint)
+              rescue => e
+                log.error("Failed to get new AWS credentials: #{e}")
+              end
             end
           end
         end