fix: stop keydown from bubbling beyond people-picker

[gavinbarron]

Closes #2891

PR Type

• Bugfix

Description of the changes

stops propagation of the keydown event from the people picker search input.

this ensures that keystrokes which might trigger in pages shortcuts in SharePoint don't reach those event listener and break the component experience.

PR checklist

• Project builds (yarn build) and changes have been tested in at least two supported browsers (Edge + non-Chromium based browser)
• All public APIs (classes, methods, etc) have been documented following the jsdoc syntax
• Stories have been added and existing stories have been tested
• Added appropriate documentation. Docs PR:

• License header has been added to all new source files (yarn setLicense)
• Contains NO breaking changes

Other information

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
mgt-components.src.components	80%	100%	0	✔
mgt-components.src.components.mgt-contact	63%	100%	0	➖
mgt-components.src.components.mgt-file	51%	100%	0	➖
mgt-components.src.components.mgt-file-list	56%	100%	0	➖
mgt-components.src.components.mgt-file-list.mgt-file-upload	49%	88%	0	❌
mgt-components.src.components.mgt-messages	66%	100%	0	➖
mgt-components.src.components.mgt-organization	47%	100%	0	❌
mgt-components.src.components.mgt-person	79%	65%	0	✔
mgt-components.src.components.mgt-person-card	64%	50%	0	➖
mgt-components.src.components.mgt-profile	40%	100%	0	❌
mgt-components.src.components.mgt-theme-toggle	100%	100%	0	✔
mgt-components.src.components.sub-components.mgt-flyout	72%	53%	0	➖
mgt-components.src.components.sub-components.mgt-spinner	100%	100%	0	✔
mgt-components.src.graph	38%	89%	0	❌
mgt-components.src.styles	92%	80%	0	✔
mgt-components.src.utils	78%	20%	0	✔
mgt-element.dist.es6.components.src.components	73%	80%	0	➖
mgt-element.dist.es6.mock.src.mock	90%	72%	0	✔
mgt-element.dist.es6.providers.src.providers	85%	69%	0	✔
mgt-element.dist.es6.src	91%	80%	0	✔
mgt-element.dist.es6.utils.src.utils	66%	69%	0	➖
mgt-element.src	88%	100%	0	✔
mgt-element.src.components	84%	100%	0	✔
mgt-element.src.mock	81%	56%	0	✔
mgt-element.src.providers	80%	85%	0	✔
mgt-element.src.utils	71%	90%	0	➖
Summary	65% (12382 / 19051)	64% (406 / 638)	0	➖