SpecializeShader should require compatible Execution Model, not ExecutionMode

In the document [_The OpenGL® Graphics System: A Specification (Version 4.6 (Core Profile) - May 5, 2022)_](https://registry.khronos.org/OpenGL/specs/gl/glspec46.core.pdf), section 7.2.1 _Shader Specialization_, the error listing reads:

> An `INVALID_OPERATION` error is generated if the `ExecutionMode` of the `OpEntryPoint` indicated by _pEntryPoint_ does not match the type of shader.

This should be _Execution Model_, not `ExecutionMode`, as in the [SPIR-V specification](https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#OpEntryPoint). While `ExecutionMode` does exist in SPIR-V, it is something else entirely.