Flaky unit tests on macOS

[Tyriar]

Flakes on macos: https://github.com/xtermjs/xterm.js/actions/runs/5913479751/job/16037928955?pr=4693

  2 failing

  1) text encodings
       StringToUtf32 decoder
         full codepoint test
           65536..0x10FFFF (surrogates):
     Error: Timeout of 20000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/xterm.js/xterm.js/out/common/input/TextDecoder.test.js)
      at processImmediate (node:internal/timers:466:21)

  2) OscParser
       OscHandlerFactory
         should work up to payload limit:
     Error: Timeout of 10000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/xterm.js/xterm.js/out/common/parser/OscParser.test.js)
      at processImmediate (node:internal/timers:466:21)

[Tyriar]

They both take ~2-3s normally, I guess the container was having problems at the time or something as all surrounded tests were much slower as well.

[Tyriar]

Other high duration tests:

StringToUtf32 decoder 
2023-08-19T21:06:13.1379420Z �[0m      full codepoint test�[0m
2023-08-19T21:06:13.2344590Z       �[32m  ✔�[0m�[90m 0..65535�[0m�[31m (1869ms)�[0m
2023-08-19T21:06:55.8027480Z �[0m    DcsHandlerFactory�[0m
2023-08-19T21:07:02.0558110Z     �[32m  ✔�[0m�[90m should work up to payload limit�[0m�[31m (6292ms)�[0m
2023-08-19T21:07:09.0790190Z     �[32m  ✔�[0m�[90m should abort for payload limit +1�[0m�[31m (7021ms)�[0m
2023-08-19T21:07:11.2216810Z �[0m    OscHandlerFactory�[0m
2023-08-19T21:07:31.8182020Z     �[32m  ✔�[0m�[90m should abort for payload limit +1�[0m�[31m (8792ms)�[0m
2023-08-19T21:07:33.6547180Z �[0m  Base64Decoder�[0m
2023-08-19T21:07:33.6648590Z �[0m    decoding�[0m
2023-08-19T21:07:38.4780730Z     �[32m  ✔�[0m�[90m 1+2 bytes�[0m�[31m (4787ms)�[0m
2023-08-19T21:07:44.5516320Z     �[32m  ✔�[0m�[90m 2+3 bytes�[0m�[31m (6067ms)�[0m
2023-08-19T21:07:53.1454150Z     �[32m  ✔�[0m�[90m 3+4 bytes�[0m�[31m (8579ms)�[0m
2023-08-19T21:07:58.9189940Z     �[32m  ✔�[0m�[90m exit on false byte�[0m�[31m (5749ms)�[0m