build: Bump Azure.Identity from 1.19.0 to 1.21.0 (#43)

---
updated-dependencies:
- dependency-name: Azure.Identity
  dependency-version: 1.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]

PetrSvihlik.Com.csproj

@@ -14,7 +14,7 @@
 
   <!-- Vulnerability overrides for transitive dependencies -->
   <ItemGroup>
-    <PackageReference Include="Azure.Identity" Version="1.19.0" />
+    <PackageReference Include="Azure.Identity" Version="1.21.0" />
     <PackageReference Include="Microsoft.Build.Tasks.Core" Version="18.6.3" />
     <PackageReference Include="Microsoft.Data.SqlClient" Version="7.0.1" />
     <PackageReference Include="Microsoft.IdentityModel.JsonWebTokens" Version="8.18.0" />