Fixes an error that is thrown when a provider is overridden in `TestBed`, if the module definition of one of the imported modules uses a function for the `imports` that is set via `setNgModuleScope`. The problem was that we have a `for...of` loop that assumes that the imports are an array, but they can also be a function. This was handled correctly in other places, but this one was missed.
Note that the above-mentioned error is only thrown at runtime when the code is transpiled to es6. In es5 TS generates a call to a helper that handles the error silently so the attached unit test only fails in es6.
Fixes#34623.
PR Close#34629
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