Update dependency Azure.Identity to 1.21.0

Author: dependencyupdates[bot]

src/Directory.Packages.props

@@ -7,7 +7,7 @@
     <PackageVersion Include="AWSSDK.CloudWatch" Version="4.0.11.2" />
     <PackageVersion Include="AWSSDK.SecurityToken" Version="4.0.7.2" />
     <PackageVersion Include="AWSSDK.SQS" Version="4.0.3.2" />
-    <PackageVersion Include="Azure.Identity" Version="1.17.0" />
+    <PackageVersion Include="Azure.Identity" Version="1.21.0" />
     <PackageVersion Include="Azure.Messaging.ServiceBus" Version="7.20.1" />
     <PackageVersion Include="Azure.Monitor.Query.Metrics" Version="1.0.0" />
     <PackageVersion Include="GitHubActionsTestLogger" Version="3.0.4" />