Fix grammar issue (#5622)

Author: saladthieves

src/platforms/common/performance/index.mdx

@@ -76,7 +76,7 @@ Automatic instrumentation for monitoring the performance of your application is
 
 ## Configure the Sample Rate
 
-Sampling for transactions must also be configured before tracing is be enabled in your app. Set the sample rate for your transactions by either:
+Sampling for transactions must also be configured before tracing is enabled in your app. Set the sample rate for your transactions by either:
 
 1. Setting a uniform sample rate for all transactions using the <PlatformIdentifier name="traces-sample-rate" /> option in your SDK config to a number between `0` and `1`. (For example, to send 20% of transactions, set <PlatformIdentifier name="traces-sample-rate" /> to `0.2`.)
 2. Controlling the sample rate based on the transaction itself and the context in which it's captured, by providing a function to the <PlatformIdentifier name="traces-sampler" /> config option.