Fix function isBase64

[leey00nsu]

Hello. Thank you for maintaining the library.

Environment

"octokit-commit-multiple-files": "^5.0.0",

Issue

When uploading an image, if the size of the base64 exceeds 5MB, the error Maximum call stack size exceeded occurs.

Changes

I found the solution here . It was an issue with the isBase64 library, and changing that function resolved the issue.

Log

Error creating commit: RangeError: Maximum call stack size exceeded
    at RegExp.test (<anonymous>)
    at isBase64 (webpack-internal:///(action-browser)/./node_modules/is-base64/is-base64.js:24:52)
    at createBlob (webpack-internal:///(action-browser)/./node_modules/octokit-commit-multiple-files/create-or-update-files.js:181:14)
    at eval (webpack-internal:///(action-browser)/./node_modules/octokit-commit-multiple-files/create-or-update-files.js:95:47)
    at Array.map (<anonymous>)
    at eval (webpack-internal:///(action-browser)/./node_modules/octokit-commit-multiple-files/create-or-update-files.js:87:45)
    at processTicksAndRejections (node:internal/process/task_queues:95:5)
Error creating commit: Maximum call stack size exceeded

[mheap]

Thank you for the PR! I've just validated locally and will release an updated version shortly