fix: escape PowerShell variable in cargo config append step (#56)

The $configPath: syntax is invalid PowerShell — the colon after
the variable name is interpreted as a drive-qualifier. Wrap in
${} to delimit the variable name.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: yeelam-gordon

build/pipelines/templates-v2/job-build-project.yml

@@ -236,7 +236,7 @@ jobs:
       replace-with = "WindowsTerminalCargo"
       "@
       Add-Content -Path $configPath -Value $registry -Encoding utf8NoBOM
-      Write-Host "Updated $configPath:"
+      Write-Host "Updated ${configPath}:"
       Get-Content $configPath
     displayName: Append Cargo registry config (CI only)