[llvm] [mlir][spirv] Add mlir-spirv-tests CI to run for mlir-spv target tests (PR #152124)

[Davide Grohmann via llvm-commits]

================
@@ -0,0 +1,31 @@
+name: MLIR SPIR-V Tests
+
+permissions:
+  contents: read
+
+on:
+  workflow_dispatch:
+  pull_request:
+    paths:
+      - 'mlir/include/mlir/Dialect/SPIRV/**'
+      - 'mlir/lib/Dialect/SPIRV/**'
+      - 'mlir/lib/Target/SPIRV/**'
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davidegrohmann wrote:

I can also add that path if preferred, but it seems a bit overkill since there are only very simple header files in there.
The reason why `mlir/include/mlir/Dialect/SPIRV/**`  is listed is due to table gen definitions mostly.

https://github.com/llvm/llvm-project/pull/152124