AUTOUIC: Fix cyclic dependency between generated UI headers and timestamp

Once the generated UI headers are created by UIC they also are involved
into processing in next run on ninja.  Autogen adds `ui_*.h` files to
the deps file `ui_*.h` and this cause timestamp start depend on `ui_*.h`.
Meanwhile `ui_*.h` depend on timestamp because of the explicit rules
added by commit 1265c65b (AUTOUIC: Collect ui header files for Ninja
generator, 2021-02-18, v3.21.0-rc1~600^2).  Avoid adding `ui_*.h` to
deps file at second ninja run.

Fixes: #16776
41 jobs for !6359 with fix_ui_headers_cycling_dependency in 12 minutes and 50 seconds (queued for 1 second)
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