rustup: update to `nightly-2025-06-23` (~1.89). #648

Job	Run time
Lint	5m 47s
Android (ubuntu-24.04, aarch64-linux-android)	8m 11s
Difftest (ubuntu-24.04)	9m 58s
Test (ubuntu-24.04)	8m 13s
Test (windows-2022)	15m 12s
Test (macOS-latest)	9m 55s
Difftest (macOS-latest)	8m 24s
Difftest (windows-2022)	17m 41s
cargo-deny	59s
Compiletest (ubuntu-24.04)	8m 37s
Compiletest (macOS-latest)	8m 49s
Compiletest (windows-2022)	15m 58s
test_success	4s
	1h 57m 48s

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