[llvm] [PAC][AArch64][llvm-readobj] Add missing tests for AUTH relocs (NFC) (PR #86511)

[Fangrui Song via llvm-commits]

MaskRay wrote:

`[test]` is stronger than `NFC` to indicate test-only changes.

You can consider: `[llvm-readobj,test] Test R_AARCH64_AUTH_{ABS64,RELATIVE}`

If you want to mention that this is previously uncovered, you can add a sentence "add missing test" to the body.

https://github.com/llvm/llvm-project/pull/86511