Regex: How to get rid of trailing newline symbol in the match?

I was looking for a regular expression that will match the first date that is NOT followed by a line that stars with 'R' letter (I want to get last commit date from git log, except for only path changing commits).

2021-12-07T16:39:43+01:00
M       test.md

2021-12-07T16:18:59+01:00
R100    old.test.md  test.md

2021-12-07T15:37:15+01:00
A       old.test.md

After a significant struggle, I get this regex (I don't care much about the date validity, I trust Git):

/20[\d-T:.Z+]+(?:\r?\n)(?!R)/

It is working quite fine – but it leaves a trailing newline character \n. No big deal, it can be repaced; but safely chaining match with replace makes the code incredibly ugly (I am using Node.js):

import { execSync } from "child_process"

const allAuthorDates = execSync(
  `git log --follow --name-status --pretty=format:%aI -- test.md`
).toString()

const lastEditExceptPathChangeDateMatch = allAuthorDates.match(
  /20[\d-T:.Z+]+(?:\r?\n)(?!R)/
)

console.log(lastEditExceptPathChangeDateMatch)

/*
[
  '2021-12-07T16:39:43+01:00\n', <-- how to get rid of that \n?
  index: 0,
  input: '2021-12-07T16:39:43+01:00\nA\ttest.md\n',
  groups: undefined
]
*/

Because of the trailing newline char, I am forced to use the horrible let result = (str.match(/…/) || [""])[0].replace(…) is there to prevent the runtime error in (probably unlikely) case the match will return null.

Would somebody be so kind to advice me how to edit the regex to get rid of the trailing \n while matching, to make the following replace unneccessary?