af: Pin Auth0.swift and its dependencies to last version that supports iOS 12

[Widcket]

• [X] All new/changed/fixed functionality is covered by tests (or N/A)
• [X] I have added documentation for all new/changed functionality (or N/A)

📋 Changes

This PR pins Auth0.swift to v2.3.2, JWTDecode.swift to v3.0.1, and SimpleKeychain to v1.0.1, which is the last version that supports iOS 12.

Otherwise, Cocoapods will automatically pull the latest version of all these libraries.

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (df82b40) 90.44% compared to head (f38357a) 90.44%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #276 +/- ## ======================================= Coverage 90.44% 90.44% ======================================= Files 48 48 Lines 471 471 ======================================= Hits 426 426 Misses 45 45 ``` | Flag | Coverage Δ | | |---|---|---| | auth0_flutter | `100.00% <ø> (ø)` | | | auth0_flutter_platform_interface | `87.03% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0#carryforward-flags-in-the-pull-request-comment) to find out more.

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