fix(ci): PowerShell variable-reference parse error in Windows verify (#201)

The 'Verify windows-latest' step in the release workflow failed on the
v0.7.3 tag with a PowerShell ParserError:

  Variable reference is not valid. ':' was not followed by a valid
  variable name character. Consider using ${} to delimit the name.

PowerShell treats $archive: as scoped-variable syntax (like $env:PATH),
so the throw-message string interpolation broke. Wrap the interpolated
variables in ${} explicitly.

The v0.7.3 release itself is unaffected — goreleaser published all 13
assets correctly. This fix prevents the same failure on future releases.

Author: charlesgreen

.github/workflows/release.yml

@@ -129,7 +129,7 @@ jobs:
           if (-not $expectedLine) { throw "no checksum entry for $archive in checksums.txt" }
           $expected = ($expectedLine -split '\s+')[0].ToLower()
           $actual = (Get-FileHash -Algorithm SHA256 $archive).Hash.ToLower()
-          if ($expected -ne $actual) { throw "checksum mismatch for $archive: expected $expected, got $actual" }
+          if ($expected -ne $actual) { throw "checksum mismatch for ${archive}: expected ${expected}, got ${actual}" }
           Write-Host "Checksum verified for $archive"
 
           Expand-Archive -Path $archive -DestinationPath .