Fix Confluence integration test failures

[lipkau]

Summary

• preserve authorization for authenticated Confluence Cloud attachment downloads that redirect through Atlassian download URLs
• update the AsPlainText integration assertion to expect entity-encoded literal wiki punctuation
• isolate the label-search integration test to the run-specific space and label

Validation

• Invoke-Pester -Path 'Tests/Functions/Invoke-Method.Tests.ps1','Tests/Functions/ConvertTo-StorageFormat.Tests.ps1','Tests/Functions/Get-Page.Tests.ps1'
• Invoke-Build -Task Build, Test

Fixes failing integration run: https://github.com/AtlassianPS/ConfluencePS/actions/runs/26500593008