fix: only show safeTxGas when present

[iamacook]

What it solves

Resolves regression.

How this PR fixes it

The safeTxGas is only show if present, meaning that it won't display for 1.3.0 Safes.

How to test it

Create a transaction on a 1.3.0 Safe and observe that the safeTxGas is not shown in the advanced gas parameters.

Screenshots

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]

Branch preview

✅ Deploy successful!

https://fix_safetxgas--webcore.review-web-core.5afe.dev

[github-actions]

ESLint Summary View Full Report

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Type	Occurrences	Fixable
Errors	0	0
Warnings	0	0
Ignored	0	N/A

• Result: ✅ success
• Annotations: 0 total

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