Use more accurate type in LinkingManager spec file

[acoates-ms]

Summary:

The LinkingModule.getInitialURL method is declared as returning a Proimise<string> but looking at the implementation it can also return null:

react-native/packages/react-native/Libraries/LinkingIOS/RCTLinkingManager.mm

Line 166 in a96272e

resolve(RCTNullIfNil(initialURL.absoluteString));

which is returned by

react-native/packages/react-native/Libraries/Linking/Linking.js

Line 96 in a96272e

getInitialURL(): Promise<?string> {

which happens to expand the type to the correct type for most external users.

React-native-window's turbomodule codegen is more type strict, and so cannot return null with the current spec.

Changelog:

[INTERNAL] [FIXED] - Use more accurate type in LinkingManager spec file

Test Plan:

Type change only, so should only affect build time change which will be caught by CI.
Have verified that this type change allows react-native-windows to return null.

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@zeyap has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

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@zeyap merged this pull request in 892c835.

[github-actions]

This pull request was successfully merged by @acoates-ms in 892c835

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