Fix broken circleci job for macOS (open-quantum-safe#305)

This PR updates the openssl version to be installed for testing macOS builds

The circleci config file currently points to [email protected] to install openssl for macOS. This change was made as
part of the following [PR](open-quantum-safe@080c3dd),
where previously `openssl@3` pointed to `openssl v3.0.x` which was causing errors trying to build oqs-provider.
So the change was made to specify `[email protected]`. OpenSSL v3.2 was released last week and the circleci jobs for
macOS started failing since `[email protected]` is no longer available to install using homebrew. Instead the following
are the options: `openssl@3` (which points to the current stable version, v3.2), `[email protected]` and `[email protected]`.

Changes made in this PR include:
- pointing the openssl version back to `openssl@3` since it now points to the latest 3.2
- a small doc change to the CONTRIBUTING doc to update the circleci command to run a specific job locally. (In the latest
  version (currently vv0.1.29314), this command does not have the --job flag)

Signed-off-by: Felipe Ventura <[email protected]>

CONTRIBUTING.md

@@ -37,7 +37,7 @@ run the following command in the project main directory prior to finishing a PR:
 If encountering CI errors in CircleCI, it may be helpful to execute the test jobs
 locally to debug. This can be facilitated by executing the command
 
-   circleci local execute --job some-test-job
+   circleci local execute [--job] some-test-job
 
 assuming "some-test-job" is the name of the test to be executed and the CircleCI
 [command line tools have been installed](https://circleci.com/docs/local-cli).