#6861
#12722

- Add a complete workflow example to `jobs.<job_id>.steps[*].if`,
  demonstrating how to skip a step if a secret is not present
- Add an explanation to "Using encrypted secrets in a workflow"
- Cross-reference the two pages

#6861
#12722 (comment)

Rather than referencing two secrets:

1. `${{ secrets.SECRET_IS_SET }}`
2. `${{ secrets.SECRET_IS_NOT_SET }}`)

This commit will update the related section of the docs to reference a
single secret (`${{ secrets.SECRET_IS_SET }}`), and will update the
`if:` conditionals to compare with empty strings as suggested.

#6861
#12722

Some `${{ }}` values were converted to `$` in the preview environment.
Adding `{% raw %}`/`{% endraw %}` will preserve the raw value.

#6861
#12722 (comment)

This PR adds an example of how to use secrets with `if:` conditionals.
The reviewer suggested comparing variable values with empty strings to
make the `if:` conditionals clearer.

Commit cecdf00 updated the secret names accordingly, but the names of
the secret and environment variable may still have been confusing.

This commit will update the secret and environment variable names to
match the cross-referenced example on the "Encrypted secrets" page.

…ions.md