[CQ]: migrate to supported Notification API

[pq]

Migrate away from slated-for-removal Notification API.

See: https://github.com/JetBrains/intellij-community/blob/b41a4084da5521effedd334e28896fd9d07410da/platform/ide-core/src/com/intellij/notification/Notification.java#L87

See: #7718.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read the Flutter Style Guide recently, and have followed its advice.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

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