Download error when running two integration tests at once

[nafg]

nafg/mill-bundler#2 was failing with

millbundler.test.downloadMillTestVersion java.nio.file.FileAlreadyExistsException: /home/runner/.cache/mill/download/0.10.9
    java.base/sun.nio.fs.UnixCopyFile.move(UnixCopyFile.java:449)
    java.base/sun.nio.fs.UnixFileSystemProvider.move(UnixFileSystemProvider.java:267)
    java.base/java.nio.file.Files.move(Files.java:1432)
    os.move$.apply(FileOps.scala:96)
    de.tobiasroeser.mill.integrationtest.MillIntegrationTestModule.$anonfun$downloadMillTestVersion$2(MillIntegrationTestModule.scala:352)
    mill.define.Task$TraverseCtx.evaluate(Task.scala:380)

(https://github.com/nafg/mill-bundler/actions/runs/3570059736/jobs/6000664632#step:5:114)

The solution was to use --jobs 1 for downloadMillTestVersion

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0e93b68..04abcb6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -27,7 +27,9 @@ jobs:
           apps: mill
 
       - name: Test
-        run: mill --no-server _.test
+        run: |
+          mill --no-server --jobs 1 __.downloadMillTestVersion 
+          mill --no-server --jobs 0 _.test
 
   publish:
     runs-on: ubuntu-latest