refactor: use sendTokensBtn instead of sendTokenButn

[Ang-dot]

What it solves

Resolves the namingly-off button variable in cypress test.

How this PR fixes it

Standardizing the naming convention for buttons as in btn. sendTokensButn -> sendTokensBtn

How to test it

Cypress tests

Build a static site:

yarn build

Serve the static files:

yarn serve

Launch the Cypress UI:

yarn cypress:open

Screenshots

Not applicable

Checklist

• I've tested the branch on mobile 📱
• I've documented how it affects the analytics (if at all) 📊
• I've written a unit/e2e test for it (if applicable) 🧑‍💻

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[Ang-dot]

I have read the CLA Document and I hereby sign the CLA

[katspaugh]

Thanks but we try to avoid making cosmetic changes like this. Please feel free to contribute more significant fixes in future.