[ci] Reduce npm update noise. (#1817)

Take only security and major version updates for the `ng-flutter`
sample.

(Similar to what's done
[here](https://github.com/flutter/packages/blob/main/.github/dependabot.yml#L33-L35))

## Issues

* Fixes https://github.com/flutter/samples/issues/1809

_See [docs about the `update-types` dependabot
setting](https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#specifying-dependencies-and-versions-to-ignore)._

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].

<!-- Links -->
[Flutter Style Guide]:
https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo
[CLA]: https://cla.developers.google.com/
[Discord]: https://github.com/flutter/flutter/wiki/Chat
[Contributors Guide]:
https://github.com/flutter/samples/blob/main/CONTRIBUTING.md

.github/dependabot.yaml

@@ -225,5 +225,6 @@ updates:
     directory: "web_embedding/ng-flutter"
     schedule:
       interval: "weekly"
-    allow:
-      - dependency-type: "direct"
+    ignore:
+      - dependency-name: "*"
+        update-types: ["version-update:semver-minor", "version-update:semver-patch"]