…ible

This commit moves the chunks of shellcode in
.github/workflows/check-by-name.yml into individual scripts.

What remains in .github/workflows/check-by-name.yml are three-line
scripts which:

  1. Dump the environment to the console
  2. Set `-x` so the following command is printed in
     properly-escaped form, which developers can simply paste to their
     own shell to reproduce the command
  3. exec() into the file containing the shellcode which previously
     comprised that step.

This ensures that if a test fails, the PR author doesn't have to
rummage around in the bowels of github in order to reproduce the
failure locally.