Release large values early for GC to be able to do its job

[kibertoad]

Summary

Currently we are observing that when importing 19 MB large file, CI eats 2 GB of memory and dies. This is not ideal.

Test plan

There is a test, showing that loading 19 MB large file does not fail GA CI.

[Siemienik]

Hi @kibertoad, Thank you for your contribution.

Yesterday we did our first "MergeFest" and there were 3 of us on the online stream. Today we plan to merge more PRs. It would be great if you could join us, you could guide us through this PR and the review would be much easier :)
Link to the event on DISCORD, on time: 3PM CEST
I also invite you to join the community on our server https://discord.gg/SNEtBKPUxE

[Siemienik]

Thank you so much for that contribution, really appreciate :)
Before merging, some timeout increase for this particular test should be done:

https://github.com/exceljs/exceljs/actions/runs/4698590205/jobs/8331063702#step:8:1739
https://github.com/exceljs/exceljs/actions/runs/4698590205/jobs/8331064811#step:8:1739

 Error: Timeout of 20000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/home/runner/work/exceljs/exceljs/spec/integration/workbook-xlsx-reader.spec.js)