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 openssl@3.1 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 `openssl@3.1`. OpenSSL v3.2 was released last week and the circleci jobs for
macOS started failing since `openssl@3.1` 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), `openssl@3.0` and `openssl@1.1`.

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 <felipe.ventura@entrust.com>

.circleci/config.yml

@@ -166,7 +166,7 @@ jobs:
       - when:
           condition:
             not:
-              equal: [ openssl@3.1, << parameters.OPENSSL_PREINSTALL >> ]
+              equal: [ openssl@3, << parameters.OPENSSL_PREINSTALL >> ]
           steps:
             - run:
                 name: Clone and build OpenSSL(3) master
@@ -186,7 +186,7 @@ jobs:
                   fi
       - when:
           condition:
-              equal: [ openssl@3.1, << parameters.OPENSSL_PREINSTALL >> ]
+              equal: [ openssl@3, << parameters.OPENSSL_PREINSTALL >> ]
           steps:
             - run:
                 name: Build OQS-OpenSSL provider

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).