tests(test): add argument value validation spec tests
Adds characterization spec tests for `deno test` argument value
validation, which previously had no coverage:
- `--fail-fast=0` is rejected (the value must be non-zero)
- `--fail-fast=-1` is rejected (not a valid non-negative integer)
- `--reporter=<invalid>` is rejected with the list of valid reporters
The existing test specs only exercise valid reporters and the happy
`--fail-fast` path. Locking in the current behavior guards against
accidentally loosening these value constraints.
