Fix chisel-plugin artifact publishing (#4648)

* Switch back to plugin cross versions rather than normal scala cross
  versions.
* Switch to Java 11 for publishing instead of Java 21 so that we can
  publish the plugin for Scala versions < 2.13.11.

Author: jackkoenig

.github/workflows/ci.yml

@@ -83,7 +83,7 @@ jobs:
       - name: Setup Scala
         uses: VirtusLab/scala-cli-setup@v1
         with:
-          jvm: adoptium:21
+          jvm: temurin:11
           apps: sbt
       - name: Publish
         run: ./mill -i io.kipp.mill.ci.release.ReleaseModule/publishAll

CONTRIBUTING.md

@@ -29,15 +29,20 @@ You can install it as described on the Chisel [installation instructions](https:
 Developers should read the Mill documentation to understand the basic commands and use.
 
 The main dependencies for development are the JDK and git.
-Any JDK 8 or newer will work for most development, but note that developing the CIRCT Panama bindings requires Java 21. 
+Any JDK 11 or newer will work for most development, but note that developing the CIRCT Panama bindings requires Java 21.
 [Coursier](https://get-coursier.io)'s command-line is useful for hot swapping JDKs.
-For example:
+For example, the following swap the JDK in your shell to the latest release of GraalVM Java 21:
 
 ```sh
 eval $(cs java --jvm graalvm-java21 --env)
 ```
 
-This will swap the JDK in your shell to the latest release of GraalVM Java 21.
+While the CIRCT Panama bindings require Java 21, publishing the Chisel plugin for versions < 2.13.11 requires Java 11.
+To switch the JDK in your shell to the latest patch release of Temurin Java 11:
+
+```sh
+eval $(cs java --jvm temurin:11 --env)
+```
 
 ### Useful commands
 

plugin/package.mill

@@ -10,7 +10,7 @@ import $file.release
 
 object `package` extends RootModule {
   // https://github.com/com-lihaoyi/mill/issues/3693
-  object cross extends Cross[Plugin](v.scalaCrossVersions)
+  object cross extends Cross[Plugin](v.pluginScalaCrossVersions)
 }
 
 trait Plugin extends CrossSbtModule with ScalafmtModule with release.ChiselPublishModule {