test: move test-exec.js out of pummel
Move test/pummel/test-exec.js to test/sequential/test-child-process-exec.js. The test does not seem to use too much resources to be put in sequential. (It does, at least as written, fail if it has too many other things to compete with, so let's leave it in sequential for now rather than parallel.)
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
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