feat: added octokitFromAuthSafe function

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🚀 Feature: Also export a function that returns | undefined, rather than throws an error, if no auth is found #7
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

💖

[github-actions]

🎉 This is included in version v0.3.0 🎉

The release is available on:

• GitHub releases
• npm package (@latest dist-tag)

Cheers! 📦🚀

[codecov]

Codecov Report

Attention: Patch coverage is 97.97980% with 2 lines in your changes missing coverage. Please review.

Project coverage is 98.73%. Comparing base (30843b4) to head (17a7a21).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/index.ts	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##              main       #8      +/-   ##
===========================================
- Coverage   100.00%   98.73%   -1.27%     
===========================================
  Files            2        5       +3     
  Lines           85      158      +73     
  Branches        16       29      +13     
===========================================
+ Hits            85      156      +71     
- Misses           0        2       +2     

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