Add 1.21.0-beta.1 version to version_client.txt (Azure#23988)

Author: jianghaolu

eng/versioning/version_client.txt

@@ -334,3 +334,4 @@ com.azure.resourcemanager:azure-resourcemanager-quota;1.0.0-beta.1;1.0.0-beta.2
 # Format;
 # beta_<groupId>:<artifactId>;dependency-version
 # note: Released beta versions will not be manipulated with the automatic PR creation code.
+beta_com.azure:azure-core;1.21.0-beta.1