Fix: Env values storing as number

[naman-bruno]

Description

Addressing issue: #3859

If a user stored any number using bru.setGlobalEnvVar or bru.setEnvVar, the GUI environment variable would stop working entirely. To resolve this issue, I have implemented typecasting of values to strings before storing them.

Contribution Checklist:

• The pull request only addresses one issue or adds one feature.
• The pull request does not introduce any breaking changes
• I have added screenshots or gifs to help explain the change if applicable.
• I have read the contribution guidelines.
• Create an issue and link to the pull request.

[pooja-bruno]

Looks good