upgrade actions/*load-artifact version to v4

[2bndy5]

This upgrade is not something dependabot can do on its own. This repo's build CI uploads multiple artifacts to under the same name. This is no longer allowed with v4. Instead, we can upload each artifact with a name unique to the version being built (ie clang-tools-v{VERSION}). then we can download all artifacts using v4 with a pattern (ie clang-tools-v*); this pattern feature was not supported in v3.

Why is this important?

actions/*load-artifact v3 uses node.js v16. This causes warnings in our CI runs about v16 to be deprecated. However, v4 uses node.js v20.