Run tests via binary version

Some modules are cross-compiled to only one Scala 3 version which needs
to be the oldest Scala 3 version, otherwise we can't make other modules
depend on it.
So we run tests by passing the binary version and let mill choose the
last available Scala version that matches

.github/workflows/actions.yml

@@ -14,7 +14,7 @@ jobs:
       fail-fast: false
       matrix:
         java-version: [8, 11]
-        scala-version: [2.12.18, 2.13.12, 3.2.2, 3.3.1]
+        scala-binary-version: [2.12, 2.13, 3]
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
@@ -23,7 +23,7 @@ jobs:
       - uses: actions/setup-java@v1
         with:
           java-version: ${{ matrix.java-version }}
-      - run: ./mill -i unitTest "${{ matrix.scala-version }}"
+      - run: ./mill -i unitTest "${{ matrix.scala-binary-version }}"
   itest:
     strategy:
       fail-fast: false
@@ -43,7 +43,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        scala-version: [2.12.18, 2.13.12, 3.2.2, 3.3.1]
+        scala-version: [2.12.18, 2.13.12, 3.2.2]
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2

build.sc

@@ -691,11 +691,15 @@ class SshdModule(val crossScalaVersion: String) extends AmmModule{
   }
 }
 
-def unitTest(scalaVersion: String) = T.command{
-  terminal(scalaVersion).test.test()()
-  amm.repl(scalaVersion).test.test()()
-  amm(scalaVersion).test.test()()
-  sshd(scalaVersion).test.test()()
+def unitTest(scalaBinaryVersion: String) = {
+  def cross[T <: AmmInternalModule](module: Cross[T]) =
+    module.items.find(_._1.head.asInstanceOf[String].startsWith(scalaBinaryVersion)).last._2
+  T.command{
+    cross(terminal).test.test()()
+    cross(amm.repl).test.test()()
+    cross(amm).test.test()()
+    cross(sshd).test.test()()
+  }
 }
 
 def integrationTest(scalaVersion: String) = T.command{