Fix refreshing progress display in the status bar

[karrtikr]

Closed with #17338

Verification steps:

• Use the latest Insiders build of the Python extension by running Python: Switch to Insiders command and reloading window.
• Activate extension by opening a Python file.
• Ensure Discovering Python Interpreters appears in the status bar while loading.
• Run Python: Select Interpreter command and click refresh icon on top right.
• Ensure Refreshing Python Interpreters appears in the status bar while refreshing.

[rchiodo]

/verified