Increase test timeout for unit tests to 40 min (#8792)

## What changed?
unit tests have been timing out recently at 20 minutes but in the
`Makefile` we use a 35 minute timeout. This PR matches the Makefile
default and allows for an extra five minutes so the test-runner program
can properly cleanup and provide output on why the timeout occurred.

## Why?
Aligning withe the `Makefile`

## How did you test it?
- [ ] built
- [ ] run locally and tested manually
- [ ] covered by existing tests
- [ ] added new unit test(s)
- [ ] added new functional test(s)

## Potential risks
Longer unit-test runs

.github/workflows/run-tests.yml

@@ -253,7 +253,7 @@ jobs:
 
       - name: Run unit tests
         timeout-minutes: 20
-        run: make unit-test-coverage
+        run: TEST_TIMEOUT=15m make unit-test-coverage
         env:
           UNIT_TEST_DIRS: ${{ inputs.unit_test_directory }}
           TEST_ARGS: ${{ needs.set-up-single-test.outputs.single_test_args }}