Make most RunModule.runXxx commands exclusive

Fix #5208

Author: lefou

libs/jvmlib/src/mill/javalib/RunModule.scala

@@ -110,7 +110,7 @@ trait RunModule extends WithJvmWorkerModule with RunModuleApi {
   /**
    * Runs this module's code in a subprocess and waits for it to finish
    */
-  def run(args: Task[Args] = Task.Anon(Args())): Task.Command[Unit] = Task.Command {
+  def run(args: Task[Args] = Task.Anon(Args())): Task.Command[Unit] = Task.Command(exclusive = true) {
     runForkedTask(finalMainClass, args)()
   }
 
@@ -120,7 +120,7 @@ trait RunModule extends WithJvmWorkerModule with RunModuleApi {
    * since the code can dirty the parent Mill process and potentially leave it
    * in a bad state.
    */
-  def runLocal(args: Task[Args] = Task.Anon(Args())): Task.Command[Unit] = Task.Command {
+  def runLocal(args: Task[Args] = Task.Anon(Args())): Task.Command[Unit] = Task.Command(exclusive = true) {
     runLocalTask(finalMainClass, args)()
   }
 
@@ -129,7 +129,7 @@ trait RunModule extends WithJvmWorkerModule with RunModuleApi {
    */
   def runMain(@arg(positional = true) mainClass: String, args: String*): Task.Command[Unit] = {
     val task = runForkedTask(Task.Anon { mainClass }, Task.Anon { Args(args) })
-    Task.Command { task() }
+    Task.Command(exclusive = true) { task() }
   }
 
   /**
@@ -148,7 +148,7 @@ trait RunModule extends WithJvmWorkerModule with RunModuleApi {
    */
   def runMainLocal(@arg(positional = true) mainClass: String, args: String*): Task.Command[Unit] = {
     val task = runLocalTask(Task.Anon { mainClass }, Task.Anon { Args(args) })
-    Task.Command { task() }
+    Task.Command(exclusive = true) { task() }
   }
 
   /**