Fix powershell SourceEnv permission failure
What does this MR do?
This adds a try/catch for Powershell's implementation of SourceEnv.
Why was this MR needed?
We discovered that occasionally the created env file can be created but cannot be read back.
It might be later that want to explicitly set permissions on this, but for now, it's possible that it's only happening due to our specific docker setup in CI.
Given this is a new feature, we'll wait for feedback and discover more setups where this isn't working as intended. For now, we'll print a warning whenever the file cannot be read.
What's the best way to test this MR?
Pipeline and tests should pass.