CI - Build with more than 2 threads

I noticed in https://github.com/KhronosGroup/SPIRV-LLVM-Translator/blob/main/.github/workflows/check-in-tree-build.yml#L122

it has `make llvm-spirv -j2`

why is this only `2`?

I was looking into how the various `KhronosGroup` repos are using our limited, shared Github CI minutes, the `SPIRV-LLVM-Translator` repo is [among the most](https://github.com/KhronosGroup/SPIRV-LLVM-Translator/actions/metrics/usage?dateRangeType=DATE_RANGE_TYPE_LAST_YEAR) but understand it is a constantly and large contributed repo

I see the CI jobs take about 55 minutes, 50 of which are just building it, looking at the Linux build, I noticed it was only using 2 threads and should just use `ninja` or `make llvm-spirv -j$(nproc)`

Thanks

Open .github/workflows/check-in-tree-build.yml around line 122 and inspect how the Linux build is configured. Check the available CI parallelism and compare the existing make command with the workflow's other build steps. Done means the build uses an appropriate thread count and the workflow still completes successfully.

Written by the indexing model from the issue text.