Github provider removed anonymous access flag

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## Describe the Bug
The Terraform Github provider was updated to remove the `anonymous` access flag. This was unfortunately done in a minor release. The current pessimistic constraint of `~> 2.2` fails, as the change appeared after 2.8.1 in 2.9.0.

See [this change](https://github.com/terraform-providers/terraform-provider-github/commit/5e9d0756b071efa05a909fcff6428010ad661181#diff-9d0b8010dc61a844fd5ffde3f9a8c38e).

## Expected Behavior
The module would continue to cleanly apply with the given constraint.

## Steps to Reproduce
Steps to reproduce the behavior:
An example can be seen in [this PR](https://github.com/cloudposse/terraform-aws-ecs-web-app/pull/52).

## Screenshots
N/A

## Environment (please complete the following information):
Terraform version: 0.12.24
Github Provider version: 2.9.0

## Additional Context
It can probably be fixed by setting the constraint to `~> 2.8.0` or `>= 2.2, <2.9`. Another potential fix is to adapt the module to use the newer provider, assuming there is equivalent functionality to the anonymous access now.

Upstream issue [here](https://github.com/terraform-providers/terraform-provider-github/issues/502), though I suspect that will result in just a clarification, and perhaps CHANGELOG change.