Don't lift the argument of a synchronized block in scoverage

compiler/src/dotty/tools/dotc/transform/InstrumentCoverage.scala

@@ -434,7 +434,7 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
          * they shouldn't be lifted.
          */
         val sym = fun.symbol
-        sym.exists && (isShortCircuitedOp(sym) || StringInterpolatorOpt.isCompilerIntrinsic(sym))
+        sym.exists && (isShortCircuitedOp(sym) || StringInterpolatorOpt.isCompilerIntrinsic(sym) || sym == defn.Object_synchronized)
       end
 
       val fun = tree.fun

tests/run/i16940.scala

@@ -0,0 +1,30 @@
+// scalac: -coverage-out:coverage
+// scalajs: --skip
+
+import concurrent.ExecutionContext.Implicits.global
+import scala.concurrent.*
+import scala.concurrent.duration.*
+
+var test = 0
+
+def brokenSynchronizedBlock(option: Boolean): Future[Unit] = Future {
+  if (option) {
+    Thread.sleep(500)
+  }
+  synchronized {
+    val tmp = test
+    Thread.sleep(1000)
+    test = tmp + 1
+  }
+}
+
+object Test extends App {
+  Await.result(
+    Future.sequence(Seq(brokenSynchronizedBlock(false), brokenSynchronizedBlock(true)))
+      .map { result =>
+        println(test)
+        assert(test == 2)
+      },
+    3.seconds
+  )
+}