Fix special cases of kwargs + TypeVarTuple #13111

Job	Run time
Test suite with Python nightly	2m 51s
Test suite with py38-ubuntu, mypyc-compiled	2m 54s
Test mypyc suite with 32-bit Python	2m 51s
Test suite with py38-windows-64	2m 41s
Test suite with py39-ubuntu	2m 53s
Test suite with py310-ubuntu	2m 52s
Test suite with py311-ubuntu, mypyc-compiled	2m 53s
Test suite with py312-ubuntu, mypyc-compiled	2m 52s
mypyc runtime tests with py39-macos	2m 53s
mypyc runtime tests with py38-debug-build-ubuntu	2m 54s
Type check our own code (py38-ubuntu)	1m 49s
Type check our own code (py38-windows-64)	2m 25s
Formatting and code style with Black + ruff	36s
	33m 24s

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