Split up testRepoSourceRoot from testRepoRoot (#4355)

Works around #4176 in Mills
own build until we can fix it for real

.github/workflows/post-build-selective.yml

@@ -73,6 +73,8 @@ jobs:
 
       - run: ./mill -i -k selective.resolve ${{ inputs.millargs }}
 
+      - run: cat out/mill-build/methodCodeHashSignatures.dest/current/spanningInvalidationTree.json
+
       - run: ./mill -i -k selective.resolveTree ${{ inputs.millargs }}
 
       - run: ./mill -i -j1 -k selective.run ${{ inputs.millargs }}

example/package.mill

@@ -211,7 +211,8 @@ object `package` extends RootModule with Module {
 
   trait ExampleCrossModule extends build.integration.IntegrationTestModule {
     // disable scalafix because these example modules don't have sources causing it to misbehave
-    def testRepoRoot: T[PathRef] = Task.Source(millSourcePath)
+    def testRepoSourceRoot: T[PathRef] = Task.Source(millSourcePath)
+    def testRepoRoot: T[PathRef] = Task{ testRepoSourceRoot() }
 
     def sources0 = Task.Sources(millSourcePath)
     def sources = Task {

readme.adoc

@@ -25,7 +25,6 @@ https://www.patreon.com/lihaoyi[image:https://img.shields.io/badge/patreon-spons
 Mill is a fast JVM build tool that supports Java and Scala. Mill aims to make your 
 project’s build process performant, maintainable, and flexible.
 
-
 If you want to use Mill in your own projects, check out our documentation:
 
 * {link-current-doc-site}[Documentation]