fix es6 tsc checks complaining on newer s regex flag

[MichaelWest22]

Description

gitlab pipeline seems to be reporting tsc error

> [email protected] types-check
> tsc src/htmx.js --noEmit --checkJs --target es6 --lib dom,dom.iterable

Error: src/htmx.js(586,79): error TS[15](https://github.com/bigskysoftware/htmx/actions/runs/11154764763/job/31004572782#step:5:16)01: This regular expression flag is only available when targeting 'es2018' or later.
Error: Process completed with exit code 2.

removing the s from the regex fixes the issue along with updating the regex to not need this flag by having [\s\S] which is all characters including newline which "." does not include unless you add the newer s flag to the regex which is only supported in 2018+ browsers.

Alternative solution is to change package.json type-check line to target es2018 or newer

"types-check": "tsc src/htmx.js --noEmit --checkJs --target es2018 --lib dom,dom.iterable",

Corresponding issue:
#2781

Testing

Ran though all head-support extension manual tests to make sure they work as expected after regex change as well as manually testing regex change in JS console

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded