Fix dumpio: true logs about translateMutations

[timvandermeij]

In PR #18260 we enabled dumpio: true for Puppeteer. This option forwards the browser logs to Node's log stream so that we can see any warnings/errors that are logged in e.g. the web console. This surfaced a few interesting issues that we should fix before we enable that further due to the spammy nature of said logs.

This issue tracks the following often repeated log from http://54.193.163.58:8877/32bb151d23ef0ea/output.txt:

JavaScript warning: http://127.0.0.1:52508/build/generic/web/viewer.mjs, line 2829: Script terminated by timeout at:
translateMutations/this.pendingrAF<@http://127.0.0.1:52508/build/generic/web/viewer.mjs:2829:40
FrameRequestCallback*translateMutations@http://127.0.0.1:52508/build/generic/web/viewer.mjs:2828:46
connectRoot/this.mutationObserver<@http://127.0.0.1:52508/build/generic/web/viewer.mjs:2766:89
MutationCallback*connectRoot@http://127.0.0.1:52508/build/generic/web/viewer.mjs:2766:31
translate@http://127.0.0.1:52508/build/generic/web/viewer.mjs:2912:18
initialize@http://127.0.0.1:52508/build/generic/web/viewer.mjs:12201:15
async*run@http://127.0.0.1:52508/build/generic/web/viewer.mjs:12477:16
webViewerLoad@http://127.0.0.1:52508/build/generic/web/viewer.mjs:14525:24
@http://127.0.0.1:52508/build/generic/web/viewer.mjs:14529:3

This is most likely Fluent code being interrupted, and it seems to show up now that we actually close the viewer correctly since PR #18271. Interestingly this mostly (but not exclusively as proven by http://54.241.84.105:8877/c9f8c7617ecd080/output.txt) shows up on the Windows bot. Did this perhaps surface a bug in the viewer's cleanup logic that we're not stopping Fluent translation correctly?