Install 7zip first to avoid bootstrap extraction issues

Installing 7zip first prevents the 7zr.exe access denied error that
occurs when Scoop tries to use its temporary extractor for other packages.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: WebKit ARM64 Builder

.github/workflows/build.yml

@@ -294,7 +294,10 @@ jobs:
             echo "$env:USERPROFILE\scoop\shims" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
           }
           
-          # Install aria2 first for parallel downloads
+          # Install 7zip first to avoid bootstrap extraction issues
+          scoop install 7zip
+          
+          # Install aria2 for parallel downloads
           scoop install aria2
           
           # Install tools via Scoop