avm2: Don't activate fast-path for non-public Multiname #26535

Job	Run time
Paths filter	7s
Test Rust stable / ubuntu-24.04	4m 43s
Test Rust stable / windows-latest	12m 8s
Test Rust stable / macos-14	3m 16s
Test Rust nightly / ubuntu-24.04	4m 47s
Check dependencies	1m 26s
Test Rust ${{ matrix.rust_version }} / ${{ matrix.os }}	0s
Test Rust beta / ubuntu-24.04	4m 36s
Lints with Rust stable	4m 27s
Lints with Rust beta	4m 43s
Lints with Rust nightly	4m 33s
	44m 46s

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