Include modified files in `--diff-filter`

[Widcket]

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

📋 Changes

This PR updates the Git diff filter used on the Git hook and the respective CI check to include modified files, so it catches changes made to the copied files: .gitignore and Podspec.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

:exclamation: No coverage uploaded for pull request base (feature/macos-support@19afea6). Click here to learn what that means.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## feature/macos-support #358 +/- ## ======================================================== Coverage ? 96.36% ======================================================== Files ? 98 Lines ? 1596 Branches ? 328 ======================================================== Hits ? 1538 Misses ? 50 Partials ? 8 ``` | [Flag](https://app.codecov.io/gh/auth0/auth0-flutter/pull/358/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0) | Coverage Δ | | |---|---|---| | [auth0_flutter](https://app.codecov.io/gh/auth0/auth0-flutter/pull/358/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0) | `100.00% <0.00%> (?)` | | | [auth0_flutter_android](https://app.codecov.io/gh/auth0/auth0-flutter/pull/358/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0) | `97.35% <0.00%> (?)` | | | [auth0_flutter_ios](https://app.codecov.io/gh/auth0/auth0-flutter/pull/358/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0) | `99.85% <0.00%> (?)` | | | [auth0_flutter_platform_interface](https://app.codecov.io/gh/auth0/auth0-flutter/pull/358/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0) | `87.03% <0.00%> (?)` | | 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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