rustup: update to `nightly-2025-06-23` (~1.89). #592

Job	Run time
Test (macOS-latest)	5m 43s
Test (ubuntu-24.04)	8m 18s
Compiletest (windows-2022)	4m 32s
Difftest (ubuntu-24.04)	9m 29s
Compiletest (ubuntu-24.04)	4m 21s
Android (ubuntu-24.04, aarch64-linux-android)	8m 38s
Lint	6m 5s
cargo-deny	1m 7s
Difftest (macOS-latest)	8m 40s
Test (windows-2022)	15m 35s
Difftest (windows-2022)	17m 13s
Compiletest (macOS-latest)	8s
test_success	2s
	1h 29m 51s

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