Update azure-core-test to 1.21.1 instead of unreleased version (Azure#37320)

Author: heyams

sdk/monitor/azure-monitor-opentelemetry-exporter/pom.xml

@@ -151,7 +151,7 @@
     <dependency>
       <groupId>com.azure</groupId>
       <artifactId>azure-core-test</artifactId>
-      <version>1.22.0-beta.1</version>  <!-- {x-version-update;unreleased_com.azure:azure-core-test;dependency} -->
+      <version>1.21.1</version>  <!-- {x-version-update;com.azure:azure-core-test;dependency} -->
       <scope>test</scope>
     </dependency>
     <dependency>