chore: Bump Azure.Identity from 1.14.0 to 1.15.0

---
updated-dependencies:
- dependency-name: Azure.Identity
  dependency-version: 1.15.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Directory.Packages.props

@@ -35,7 +35,7 @@
     <!-- Replace vulnerable AzureKeyVault package with modern Azure SDK -->
     <PackageVersion Include="Azure.Extensions.AspNetCore.Configuration.Secrets" Version="1.4.0" />
     <PackageVersion Include="Azure.Security.KeyVault.Secrets" Version="4.7.0" />
-    <PackageVersion Include="Azure.Identity" Version="1.14.0" />
+    <PackageVersion Include="Azure.Identity" Version="1.15.0" />
     <!-- Validation -->
     <PackageVersion Include="FluentValidation" Version="12.0.0" />
     <PackageVersion Include="FluentValidation.AspNetCore" Version="11.3.1" />