fix(capacitor): replace deprecated platform check method (#30195)

Issue number: resolves internal

ref: https://github.com/ionic-team/capacitor/issues/7884

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## What is the current behavior?
`this.platform.is('capacitor')` returns `false` in Capacitor App.

## What is the new behavior?
`this.platform.is('capacitor')` returns as expected.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

## Other information
It might also need to be fixed.


https://github.com/ionic-team/ionic-framework/blob/14b6538d98303cb753d881ec6978fb98f53ed54c/core/src/utils/test/platform.utils.ts#L32

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Co-authored-by: ShaneK <shane@shanessite.net>