Rollup merge of #103709 - cuviper:netbsd-9, r=pietroalbini

Rollup merge of #103709 - cuviper:netbsd-9, r=pietroalbini

ci: Upgrade dist-x86_64-netbsd to NetBSD 9.0

This is another step in toolchain upgrades for LLVM 16, which will need at least GCC 7.1.

Our previous NetBSD 8.0 cross-toolchain used its system GCC 5.5. While there are newer versions available in pkgsrc, I could not get those working for cross-compilation. Upgrading to NetBSD 9.0 gets us GCC 7.4, which is sufficient for now.

This will affect the compatibility of the build we ship for `x86_64-unknown-netbsd`, but others may still build their own from source if that is needed. It is expected that NetBSD 8 will reach EOL soon anyway, approximately one month after 10 is released, but there is no firm date for that.