Catch correct exception when trying to access step context

[schustmi]

Describe changes

During the StepContext rework, the StepEnvironment was replaced by the get_step_context() function to get the pipeline/run name. We used a try...except block to catch the KeyError that occurred when we're not running inside a pipeline step, but this now needs to be a RuntimeError to work with the new get_step_context().

Pre-requisites

Please ensure you have done the following:

• I have read the CONTRIBUTING.md document.
• If my change requires a change to docs, I have updated the documentation accordingly.
• If I have added an integration, I have updated the integrations table and the corresponding website section.
• I have added tests to cover my changes.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Other (add details above)