rustup: update to `nightly-2025-06-23` (~1.89). #638

Job	Run time
Android (ubuntu-24.04, aarch64-linux-android)	4m 36s
Compiletest (ubuntu-24.04)	2m 53s
Compiletest (windows-2022)	3m 5s
Difftest (ubuntu-24.04)	3m 54s
Difftest (windows-2022)	3m 50s
Compiletest (macOS-latest)	2m 50s
Difftest (macOS-latest)	3m 32s
Test (macOS-latest)	2m 28s
Lint	4m 43s
Test (ubuntu-24.04)	2m 50s
Test (windows-2022)	2m 48s
cargo-deny	1m 6s
test_success	3s
	38m 38s

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