rustup: update to `nightly-2025-06-23` (~1.89). #584

Job	Run time
cargo-deny	1m 26s
Lint	5m 16s
Test (windows-2022)	14m 58s
Test (macOS-latest)	10m 18s
Difftest (ubuntu-24.04)	10m 12s
Difftest (windows-2022)	16m 59s
Compiletest (windows-2022)	3m 48s
Test (ubuntu-24.04)	8m 6s
Android (ubuntu-24.04, aarch64-linux-android)	8m 26s
Difftest (macOS-latest)	9m 1s
Compiletest (ubuntu-24.04)	3m 51s
Compiletest (macOS-latest)	3m 36s
test_success	3s
	1h 36m 0s

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