Update toolchain to `nightly-2023-09-05` #5279

Job	Run time
benchcomp-tests	10m 48s
perf	45m 52s
bookrunner	27m 31s
regression (macos-11)	44m 56s
regression (ubuntu-20.04)	29m 22s
regression (ubuntu-22.04)	32m 45s
releasebundle-macos (macos-11)	10m 8s
releasebundle-ubuntu	38m 2s
write-json-symtab-regression	21m 43s
	4h 21m 7s

Provide feedback