lit_test : check if there is already a deps key in kwargs (#87290)

This change checks if there is already a `deps` key in `kwargs` and
concatenate it to avoid multiple values for `deps` key argument.

background:
https://github.com/llvm/llvm-project/pull/87022 recently added explicit
`deps` to the lit_test. This is causing StableHLO bazel build failures
at
https://github.com/openxla/stablehlo/actions/runs/8511888283/job/23312383380?pr=2147

Tested: local build run is successful