fix: flakey tracer provider test (#834)

The logger was sometimes receiving a debug message from the tracer provider
when it was being upgraded.  Setting the log level to warn remedies that
as the test is concerned with not receiving a warning log.

sdk/test/opentelemetry/sdk/trace/tracer_provider_test.rb

@@ -143,7 +143,7 @@
     before do
       @log_stream = StringIO.new
       @_logger = OpenTelemetry.logger
-      OpenTelemetry.logger = ::Logger.new(@log_stream)
+      OpenTelemetry.logger = ::Logger.new(@log_stream, level: 'WARN')
     end
 
     after do