Fix Incident - deprecation warning incorrectly displayed

[tonykploomber]

Describe your changes

Fix the bug - deprecation warning incorrectly displayed

Originally, we have the custom variable substitution, but it will also handle the connection string like this, which we have the regex to detect if it's contains :variable, it will detect connection string as variable substitution case.

Connection string:
mysql+mysqldb://user:password@127.0.0.1:3306/db

(:password was treat as variable)

Fix by executing the _var_expand after the command is parsed by parse.parse(), so it would not contain connecting string anymore

Issue ticket number and link

Closes #203

Checklist before requesting a review

• I have performed a self-review of my code
• I have added thorough tests (when necessary).
• I have added the right documentation in the docstring and changelog (when needed)

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📚 Documentation preview 📚: https://jupysql--213.org.readthedocs.build/en/213/