ci: increase dev drive size

For working around linked errors:
https://github.com/astral-sh/uv/actions/runs/10371457087/job/28711821180?pr=5887

Author: BurntSushi

.github/workflows/ci.yml

@@ -228,7 +228,7 @@ jobs:
     steps:
       - name: Create Dev Drive using ReFS
         run: |
-          $Volume = New-VHD -Path C:/uv_dev_drive.vhdx -SizeBytes 14GB |
+          $Volume = New-VHD -Path C:/uv_dev_drive.vhdx -SizeBytes 20GB |
                     Mount-VHD -Passthru |
                     Initialize-Disk -Passthru |
                     New-Partition -AssignDriveLetter -UseMaximumSize |