rustup: update to `nightly-2025-06-23` (~1.89). #661

Job	Run time
Android (ubuntu-24.04, aarch64-linux-android)	8m 13s
Test (macOS-latest)	8m 23s
Test (windows-2022)	14m 55s
Compiletest (windows-2022)	16m 21s
Test (ubuntu-24.04)	8m 3s
Compiletest (macOS-latest)	5m 3s
Compiletest (ubuntu-24.04)	8m 20s
Lint	6m 5s
Difftest (ubuntu-24.04)	9m 6s
Difftest (windows-2022)	16m 45s
cargo-deny	57s
Difftest (macOS-latest)	6m 29s
test_success	4s
	1h 48m 44s

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