Environment variable definitions file substitution does not work when debugging a Python file

Environment data

• VS Code version: Code 1.34.0 (a622c65b2c713c890fcf4fbf07cf34049d5fe758, 2019-05-15T21:59:37.030Z)
• Extension version (available under the Extensions sidebar): 2019.4.12954
• OS and version: Windows x64 10.0.17763
• Python version (& distribution if applicable, e.g. Anaconda): 3.6
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): venv

Expected behaviour

According to documentation the value of any existing environment variable could be used when defining an environment variables.

Actual behaviour

Value of PATH environment variable is not being substituted.

Steps to reproduce:

1. Create .env file with a single line PATH="${PATH};Blah-blah-blah".
2. Print PATH value with print(os.environ.get('PATH'))
3. ;Blah-blah-blah gets printed.