tests(binary): improve readability of multiline strings

[ee7]

This commit indents multiline string literals in the tests of the
configlet executable, which makes the tests easier to follow visually.

We also replace a dedent with the simpler unindent.

---

Example before this PR:

    test "after syncing, another `sync --update --mode=include` performs no changes":
      execAndCheck(0):
        execCmdEx(&"{binaryPath} -t {trackDir} sync --update -mi -o -p {psDir}")

      check outp == """
Syncing exercises...
All exercises are synced!
"""

    test "after syncing, a `sync` without `--update` shows that exercises are up to date":
      execAndCheck(0):
        execCmdEx(&"{binaryPath} -t {trackDir} sync -o -p {psDir}")
      check outp == """
Checking exercises...
All exercises are up-to-date!
"""

With this PR:

    test "after syncing, another `sync --update --mode=include` performs no changes":
      execAndCheck(0):
        execCmdEx(&"{binaryPath} -t {trackDir} sync --update -mi -o -p {psDir}")

      check outp == """
        Syncing exercises...
        All exercises are synced!
      """.unindent()

    test "after syncing, a `sync` without `--update` shows that exercises are up to date":
      execAndCheck(0):
        execCmdEx(&"{binaryPath} -t {trackDir} sync -o -p {psDir}")
      check outp == """
        Checking exercises...
        All exercises are up-to-date!
      """.unindent()

---

Another tiny PR. I'm making this PR separately from #366 in the hopes of making its eventual squashed commit marginally more comprehensible.

Obscure implementation detail: strutils.dedent can only be used with & from std/strformat if the indendation amount is passed.