fix(metro-serializer-esbuild): don't block on metafile write

[tido64]

Description

Don't block when writing metafile

Test plan

Configure metafile:

diff --git a/packages/test-app/package.json b/packages/test-app/package.json
index 794bc85ea..a21504159 100644
--- a/packages/test-app/package.json
+++ b/packages/test-app/package.json
@@ -128,7 +128,9 @@
         "id": "esbuild",
         "entryFile": "src/index.ts",
         "assetsDest": "dist",
-        "treeShake": true,
+        "treeShake": {
+          "metafile": "metafile.json"
+        },
         "plugins": [
           "@rnx-kit/metro-plugin-cyclic-dependencies-detector",
           [

Bundle:

% yarn bundle+esbuild --dev false --platform ios
info Bundling ios...
                Welcome to Metro v0.83.2
              Fast - Scalable - Integrated


info esbuild bundle size: 821468
info Writing esbuild metafile to: metafile.json
info Writing bundle output to: dist/main+esbuild.ios.jsbundle
info Writing sourcemap output to: dist/main+esbuild.ios.jsbundle.map
info Done writing esbuild metafile
info Done writing bundle output
info Done writing sourcemap output