Set balance below existential

[faculerena]

Summary

• [M] y/n | Does it introduce breaking changes?
• [N] y/n | Is it dependant on the specific version of cargo-contract or pallet-contracts?

Added a check for setting the balance in tests below the existential minimum

Description

Given that accounts with a balance below the existential minimum get reaped, adding a check to prohibit setting balance below seems logical. If this should not be like this, feel free to correct us.

Checklist before requesting a review

• [X] My code follows the style guidelines of this project
• [x] I have added an entry to CHANGELOG.md
• [X] I have commented my code, particularly in hard-to-understand areas
• [x] I have added tests that prove my fix is effective or that my feature works
• [X] Any dependent changes have been merged and published in downstream modules

[SkymanOne]

Please merge master