Address auth ALC review comments

[PrzemyslawKlys]

Changes proposed in this pull request

• Guard assemblyName.Name before using it in the managed ALC resolver.
• Use Import-Module -LiteralPath for the Desktop/no-ALC fallback path.
• Relax the worker-thread dependency resolution test so it does not assume Azure.Core is absent from AssemblyLoadContext.Default.

Why

This addresses the inline Copilot review comments from #3633 and the earlier test flakiness concern from #3632.

The production resolver should treat a missing assembly name as an ordinary resolution miss and return null. The Desktop fallback should import the exact DLL path instead of allowing wildcard interpretation. The test only needs to prove that the dependency resolved by the worker thread lands in the same non-default Graph authentication ALC; it should not fail merely because another test loaded Azure.Core in the default context.

Validation

• pwsh -NoProfile -Command 'Invoke-Pester .\src\Authentication\Authentication\test\Microsoft.Graph.Authentication.Tests.ps1 -Output Detailed'
  • 8 tests passed
• PowerShell parser validation for Microsoft.Graph.Authentication.psm1
• git diff --check

Other links

• Follow-up to Isolate Graph authentication assembly loading (#3632) #3633
• Addresses Isolate Graph authentication assembly loading (#3632) #3633 Copilot comments:
  • Isolate Graph authentication assembly loading (#3632) #3633 (comment)
  • Isolate Graph authentication assembly loading (#3632) #3633 (comment)
• Also addresses earlier Copilot test-flakiness concern from Isolate Microsoft.Graph.Authentication assembly loading #3632:
  • Isolate Microsoft.Graph.Authentication assembly loading #3632 (comment)