contributing: MongoDb extension on Mac M1

[Chris53897]

Preconditions

Following the Contribute-Guide https://github.com/liip/LiipTestFixturesBundle/blob/2.x/doc/contributing.md
does not install MongoDb extension on Mac M1. I am not sure about other OS.

Steps to reproduce

Follow the guide above

Expected result

Correct local test environment.

Actual result

Error about missing MongoDb extension

[alexislefebvre]

I don't have a M1 to test, but it may work: bitnami/containers#40947 (comment)

You can keep this change on your local environment without pushing it.

[Chris53897]

@alexislefebvre Thanks, I will have a look at this and the PR as soon as if i have some free time.