refactor: update enum types to remove duplicate member values (backport

aws#19320) (aws#20932)

This is an automatic backport of pull request aws#19320 done by [Mergify](https://mergify.com).
Cherry-pick of b0346a4 has failed:
```
On branch mergify/bp/main/pr-19320
Your branch is up to date with 'origin/main'.

You are currently cherry-picking commit b0346a4.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   packages/@aws-cdk/aws-ec2/lib/instance-types.ts
	modified:   packages/@aws-cdk/aws-ec2/lib/machine-image.ts
	modified:   packages/@aws-cdk/aws-ec2/lib/port.ts
	modified:   packages/@aws-cdk/aws-ec2/lib/util.ts
	modified:   packages/@aws-cdk/aws-ec2/test/instance.test.ts

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   packages/@aws-cdk/aws-ec2/lib/vpc.ts
	both modified:   packages/@aws-cdk/aws-ec2/lib/windows-versions.ts

```


To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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