Update autofill to 8.4.2 (#3642)

Task/Issue URL:
https://app.asana.com/0/1205691418983700/1205691418983700
Autofill Release:
https://github.com/duckduckgo/duckduckgo-autofill/releases/tag/8.4.2


## Description
Updates Autofill to version
[8.4.2](https://github.com/duckduckgo/duckduckgo-autofill/releases/tag/8.4.2).

### Autofill 8.4.2 release notes
## What's Changed
* Ema/perf followups by @GioSensation in
duckduckgo/duckduckgo-autofill#386
* Fix handler regression by @GioSensation in
duckduckgo/duckduckgo-autofill#392
* Bump markdown-it from 13.0.1 to 13.0.2 by @dependabot in
duckduckgo/duckduckgo-autofill#388
* Revert mutation observer for forms by @GioSensation in
duckduckgo/duckduckgo-autofill#396


**Full Changelog**:
duckduckgo/duckduckgo-autofill@8.4.1...8.4.2

## Steps to test
This release has been tested during autofill development. For smoke test
steps see [this
task](https://app.asana.com/0/1198964220583541/1200583647142330/f).

Co-authored-by: GioSensation <[email protected]>