Avoid .incremental.dill.incremental.dill in temporary file name (#3675)

diff --git a/lib/src/dart.dart b/lib/src/dart.dart
index 1ff10dc..d846916 100644
--- a/lib/src/dart.dart
+++ b/lib/src/dart.dart
@@ -129,7 +129,7 @@
     // To avoid potential races we copy the incremental data to a temporary file
     // for just this compilation.
     final temporaryIncrementalDill =
-        p.join(tempDir, '${p.basename(incrementalDillPath)}.incremental.dill');
+        p.join(tempDir, '${p.basename(incrementalDillPath)}.temp');
     try {
       if (fileExists(incrementalDillPath)) {
         copyFile(incrementalDillPath, temporaryIncrementalDill);