fix(cli-integ): atmosphere credentials not used when profile is set via AWS_PROFILE

[iliapolo]

In CodeBuild, our initial credentials are configured via a profile ~/.aws/config and set via the AWS_PROFILE env variable.
This in turn causes the SDK to prefer the profile credentials, even after acquiring an atmosphere environment that provides static env creds:

@aws-sdk/credential-provider-node - defaultProvider::fromEnv WARNING:
--
741 | Multiple credential sources detected:
742 | Both AWS_PROFILE and the pair AWS_ACCESS_KEY_ID/AWS_SECRET_ACCESS_KEY static credentials are set.
743 | This SDK will proceed with the AWS_PROFILE value.
744 |  
745 | However, a future version may change this behavior to prefer the ENV static credentials.
746 | Please ensure that your environment only sets either the AWS_PROFILE or the
747 | AWS_ACCESS_KEY_ID/AWS_SECRET_ACCESS_KEY pair.

To fix, lets unset the AWS_PROFILE variable if/when static env creds are used.