fix: Unit Test Requires "test" Binary

[CoshUS]

Issue

The following tests do not mock path resolution which requires the system to have the binary "test".

• tests/unit/test_workflow.py::TestBaseWorkflow_run::test_must_raise_if_action_crashed
• tests/unit/test_workflow.py::TestBaseWorkflow_run::test_must_raise_if_action_failed
• tests/unit/test_workflow.py::TestBaseWorkflow_run::test_must_raise_with_no_actions
• tests/unit/test_workflow.py::TestBaseWorkflow_run::test_supply_executable_path

Error:

self = Workflow=MyWorkflow
Actions=
        <Mock name='mock.action1' id='1800480812144'>
        <Mock name='mock.action2' id='1800480812384'>
        <Mock name='mock.action3' id='1800480812240'>
args = (), kwargs = {}, valid_paths = {}, invalid_paths = {'test': []}, binary = 'test', binary_checker = <aws_lambda_builders.binary_path.BinaryPath object at 0x000001A33504EE50>

    @functools.wraps(func)
    def wrapper(self, *args, **kwargs):
        valid_paths = {}
        invalid_paths = {}
        # NOTE: we need to access binaries to get paths and resolvers, before validating.
        for binary, binary_checker in self.binaries.items():
            invalid_paths[binary] = []
            try:
                exec_paths = (
                    binary_checker.resolver.exec_paths
                    if not binary_checker.path_provided
                    else binary_checker.binary_path
                )
            except ValueError as ex:
>               raise WorkflowFailedError(workflow_name=self.NAME, action_name="Resolver", reason=str(ex))
E               aws_lambda_builders.exceptions.WorkflowFailedError: MyWorkflow:Resolver - Path resolution for runtime: runtime of binary: test was not successful

This is fine for AppVeyor as "test" exists for Unix systems or Windows with Git installed in a certain way. However, on systems without "test" binary, unit tests will fail.

Get-Command test
CommandType     Name                                               Version    Source                                                                                                                                                 
-----------     ----                                               -------    ------                                                                                                                                                 
Application     test.exe                                           0.0.0.0    C:\Program Files\Git\usr\bin\test.exe   

Description of changes:
Mocks all binary verification for workflow to better adhere to unit testing principles.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.