bugfix: Try to fix Mill flaky test

My guess is that the test failed because it takes a while for the build server to connect. Let's see if this helps.

metals/src/main/scala/scala/meta/internal/metals/MetalsLspService.scala

@@ -1029,6 +1029,7 @@ class MetalsLspService(
       }
     } else {
       buildServerPromise.future.flatMap { _ =>
+        scribe.info("Build server promise finished")
         def load(): Future[Unit] = {
           val compileAndLoad =
             Future.sequence(

tests/slow/src/test/scala/tests/mill/MillServerCodeLensSuite.scala

@@ -1,11 +1,15 @@
 package tests.mill
 
+import java.util.concurrent.TimeUnit
+
 import scala.concurrent.duration.Duration
 
+import scala.meta.internal.metals.MetalsEnrichments._
 import scala.meta.internal.metals.ServerCommands
 import scala.meta.internal.metals.{BuildInfo => V}
 
 import tests.BaseCodeLensLspSuite
+import tests.MetalsTestEnrichments._
 import tests.MillBuildLayout
 import tests.MillServerInitializer
 
@@ -14,8 +18,15 @@ class MillServerCodeLensSuite
 
   override def munitTimeout: Duration = Duration("4min")
 
+  override def afterEach(context: AfterEach): Unit = {
+    super.afterEach(context)
+    scribe.info(workspace.resolve(".metals/bsp.trace.json").text)
+  }
   test("run-mill-lens", maxRetry = 3) {
+
     cleanWorkspace()
+    val bsp = workspace.resolve(".metals/bsp.trace.json")
+    bsp.touch()
     writeLayout(
       MillBuildLayout(
         """|/MillMinimal/src/Main.scala
@@ -40,6 +51,8 @@ class MillServerCodeLensSuite
       _ <- server.initialize()
       _ <- server.initialized()
       _ <- server.executeCommand(ServerCommands.GenerateBspConfig)
+      _ <- server.server.indexingPromise.future
+        .withTimeout(2, TimeUnit.MINUTES)
       _ <- server.didOpen("MillMinimal/src/Main.scala")
       _ <- server.didSave("MillMinimal/src/Main.scala")(identity)
       _ = assertNoDiagnostics()