feat: bump firebase iOS SDK to v11.6.0

[russellwheatley]

Description

• 1 auth test failing because error code returned when using emulator isn't the same as when running live. It should be invalid-phone-number but it is returning internal-error. The underlying exception is "identitytoolkit.getRecaptchaConfig is not implemented in the Auth Emulator."
• Another test failing which is also down to this underlying exception: "identitytoolkit.getRecaptchaConfig is not implemented in the Auth Emulator." It shouldn't be failing at all but it seems setting appVerificationDisabledForTesting isn't respected as it should be.

This issue is being tracked on the firebase-ios-sdk here: firebase/firebase-ios-sdk#14242

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