[mlir][linalg][nfc] Rename test files for linalg.{un}pack

Following on from llvm#123902, removes "tensor" from test file names for
`linalg.pack` and `linalg.unpack` (which prior to llvm#123902 were Tensor
dialect Ops).

To minimize PR noise, I am submitting this without a review. However,
please ping me if you believe this or similar changes should be reviewed
before merging.

Author: banach-space