ruby: disable yjit on cross
Fix `nix build .#pkgsCross.aarch64-multiplatform.ruby` failing
with:
```
partial linking yjit/target/release/libyjit.a into yjit/target/release/libyjit.o
/nix/store/…/bin/aarch64-unknown-linux-gnu-ld: yjit/target/release/libyjit.a(yjit.1fllkjkj80qowi7xzzkaw1xy8.rcgu.o): Relocations in generic ELF (EM: 62)
/nix/store/…/bin/aarch64-unknown-linux-gnu-ld: yjit/target/release/libyjit.a(yjit.1fllkjkj80qowi7xzzkaw1xy8.rcgu.o): Relocations in generic ELF (EM: 62)
/nix/store/…/bin/aarch64-unknown-linux-gnu-ld: yjit/target/release/libyjit.a(yjit.1fllkjkj80qowi7xzzkaw1xy8.rcgu.o): error adding symbols: file in wrong format
```
Co-authored-by: Sandro <sandro.jaeckel@gmail.com>