fix: add cleanup for timeout in announce

[smhigley]

Adds cleanup for the timeout set up for announce(), for if the announcer is unmounted while there's an existing timeout.

Ref: #31251 (comment)

[codesandbox-ci]

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[fabricteam]

Perf Analysis (@fluentui/react-components)

Scenario	Render type	Master Ticks	PR Ticks	Iterations	Status
FluentProviderWithTheme	virtual-rerender	38	40	10	Possible regression

All results

Scenario	Render type	Master Ticks	PR Ticks	Iterations	Status
Avatar	mount	628	666	5000
Button	mount	317	307	5000
Field	mount	1132	1103	5000
FluentProvider	mount	714	727	5000
FluentProviderWithTheme	mount	88	88	10
FluentProviderWithTheme	virtual-rerender	38	40	10	Possible regression
FluentProviderWithTheme	virtual-rerender-with-unmount	79	75	10
MakeStyles	mount	882	873	50000
Persona	mount	1737	1761	5000
SpinButton	mount	1377	1356	5000
SwatchPicker	mount	1565	1510	5000

[fabricteam]

📊 Bundle size report

Package & Exports	Baseline (minified/GZIP)	PR	Change
react-components react-components: entire library	1.166 MB 280.364 kB	1.166 MB 280.37 kB	23 B 6 B

Unchanged fixtures

Package & Exports	Size (minified/GZIP)
react-accordion Accordion (including children components)	101.791 kB 30.819 kB
react-alert Alert	84.099 kB 23.645 kB
react-avatar Avatar	50.537 kB 16.11 kB
react-avatar AvatarGroup	20.107 kB 7.973 kB
react-avatar AvatarGroupItem	65.191 kB 20.441 kB
react-breadcrumb @fluentui/react-breadcrumb - package	117.668 kB 32.416 kB
react-button Button	39.917 kB 11.339 kB
react-button CompoundButton	47.278 kB 12.834 kB
react-button MenuButton	44.698 kB 12.729 kB
react-button SplitButton	52.71 kB 14.313 kB
react-button ToggleButton	56.963 kB 13.243 kB
react-card Card - All	104.845 kB 29.585 kB
react-card Card	97.858 kB 27.837 kB
react-card CardFooter	14.375 kB 5.796 kB
react-card CardHeader	16.618 kB 6.555 kB
react-card CardPreview	14.418 kB 5.931 kB
react-combobox Combobox (including child components)	106.032 kB 34.071 kB
react-combobox Dropdown (including child components)	107.447 kB 34.045 kB
react-components react-components: Button, FluentProvider & webLightTheme	71.955 kB 20.772 kB
react-components react-components: Accordion, Button, FluentProvider, Image, Menu, Popover	222.188 kB 62.744 kB
react-components react-components: FluentProvider & webLightTheme	44.442 kB 14.607 kB
react-datepicker-compat DatePicker Compat	228.881 kB 63.703 kB
react-dialog Dialog (including children components)	100.597 kB 30.053 kB
react-menu Menu (including children components)	154.746 kB 46.327 kB
react-menu Menu (including selectable components)	157.432 kB 46.888 kB
react-message-bar MessageBar (all components)	24.608 kB 9.155 kB
react-persona Persona	57.428 kB 17.99 kB
react-popover Popover	129.074 kB 40.438 kB
react-portal-compat PortalCompatProvider	8.39 kB 2.64 kB
react-table DataGrid	169.681 kB 47.067 kB
react-table Table (Primitives only)	46.175 kB 14.35 kB
react-table Table as DataGrid	138.765 kB 37.41 kB
react-table Table (Selection only)	77.181 kB 20.767 kB
react-table Table (Sort only)	75.824 kB 20.369 kB
react-tag-picker @fluentui/react-tag-picker - package	189.079 kB 55.943 kB
react-tags InteractionTag	15.703 kB 6.253 kB
react-tags Tag	29.408 kB 9.593 kB
react-tags TagGroup	82.895 kB 24.635 kB
react-timepicker-compat TimePicker	108.051 kB 35.451 kB
react-toast Toast (including Toaster)	99.518 kB 30.001 kB

_{🤖 This report was generated against c621c5b9d824a41d68328dd61457cf301236ddf6}

[khmakoto]

CI is complaining about the lack of a change file.