Fix: Handle all valid ST characters

[llimllib]

There is no OSC spec, but it appears that most emulators accept 0x1B 0x5C as an ST character, with 0x07 and 0x9C as alternatives with a bit less support.

This PR updates the regular expression to match all three of 0x1b 0x5C, 0x07, and 0x9C as an ST character, and updates the test file accordingly.

Choices I made, any of which I'm happy to change if you prefer:

• I did not pull out the ST character part of the regular expression into a variable, though I would prefer that, because it didn't seem to match the style of the code that's already there
• I did make the ST character into an array and loop over it in the tests, because that seemed the clearest. I can change it if you prefer
• I did not add any comments with links to relevant documentation, because it seemed out of line with the style of the code

Closes #56

[llimllib]

The tests have passed, but I think that tsd is failing on irrelevant things that I don't understand?

[sindresorhus]

I did not pull out the ST character part of the regular expression into a variable, though I would prefer that

Yeah, do that.

[llimllib]

done, and merged main too. Thanks for fixing that up