Fix special cases of kwargs + TypeVarTuple #13288

Job	Run time
Test suite with py38-ubuntu, mypyc-compiled	18m 0s
Test mypyc suite with 32-bit Python	6m 39s
Test suite with py38-windows-64	20m 28s
Test suite with py39-ubuntu	18m 43s
Test suite with py310-ubuntu	15m 58s
Test suite with py311-ubuntu, mypyc-compiled	15m 32s
Test suite with py312-ubuntu, mypyc-compiled	18m 1s
Test suit with py313-dev-ubuntu, mypyc-compiled	20m 41s
mypyc runtime tests with py39-macos	7m 12s
mypyc runtime tests with py38-debug-build-ubuntu	4m 1s
Type check our own code (py38-ubuntu)	1m 50s
Type check our own code (py38-windows-64)	2m 30s
Formatting and code style with Black + ruff	34s
	2h 30m 9s

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