Make intel build required to pass CI

[edwardhartnett]

This was a bit tricky. We had an intel build, but it was not marked as "required" to pass by GitHub, and we need it to be.

But when I tried to add it to the list of required builds, it did not appear in the dropdown list.

Turns out, we need to use different names for our builds in different workflows. For example, here's a section from our main workflow, with GNU:

jobs:
  build:
    runs-on: ubuntu-20.04

This is called "build" by the CI system. By reusing the same code in the Intel workflow file, it got the same name, "build". Then I changed the intel one to intel_build:

jobs:
  intel_build:
    runs-on: ubuntu-latest

Now "intel_build" appears on the GitHub dropdown list of available builds, and I can require that it pass before PRs are merged.

@kgerheiser you may wish to take note of this peculiarity...