UI Toolkit UI only works when assigning project wide action asset map

Steps to reproduce:

1. 

2. 

3. upgrade to 1.8.1 package version

Alternative steps to reproduce:

1. Open any existing project that contains Input System package on trunk

Actual results: UI toolkit UI doesn't work

Expected results: it just continues to work

Workaround: assign a project wide action map in Input System settings

Reproducible with versions: 1.8

Not reproducible with versions: 1.7 

Can’t test with versions: 

Tested on (OS): 

Notes:

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