Fix check issues

[gadenbuie]

Dear maintainer,

Please see the problems shown on
https://cran.r-project.org/web/checks/check_results_learnr.html.

Please correct before 2025-11-12 to safely retain your package on CRAN.

The CRAN Team

and from a follow-up message

It looks like this is failing on platforms which use the default R CMD
check and not those which use --as-cran (and hence
R_CHECK_SUGGESTS_ONLY=true).

[gadenbuie]

Check Details
Version: 0.11.5
Check: tests
Result: ERROR 
    Running ‘testthat.R’ [84s/395s]
  Running the tests in ‘tests/testthat.R’ failed.
  Complete output:
    > 
    > if (requireNamespace("testthat")) {
    +   library(testthat)
    +   library(learnr)
    + 
    +   test_check("learnr")
    + }
    Loading required namespace: testthat
    [ FAIL 1 | WARN 1 | SKIP 18 | PASS 822 ]
    
    ══ Skipped tests (18) ══════════════════════════════════════════════════════════
    • On CRAN (18): 'test-available-tutorials.R:17:3', 'test-evaluators.R:2:3',
      'test-evaluators.R:92:3', 'test-evaluators.R:137:3',
      'test-evaluators.R:179:3', 'test-evaluators.R:212:3',
      'test-evaluators.R:244:3', 'test-evaluators.R:279:3',
      'test-evaluators.R:363:3', 'test-exercise.R:367:3', 'test-exercise.R:1237:3',
      'test-exercise.R:1377:3', 'test-exercise.R:1426:3', 'test-exercise.R:1444:3',
      'test-exercise.R:1472:3', 'test-exercise.R:1535:3',
      'test-shinytest2-aaa.R:2:1', 'test-shinytest2-hints.R:2:1'
    
    ══ Failed tests ════════════════════════════════════════════════════════════════
    ── Failure ('test-auto-complete.R:3:3'): R auto complete finds runif vars ──────
    auto_complete_r("method not found") not equal to list().
    Length mismatch: comparison on first 0 components
    
    [ FAIL 1 | WARN 1 | SKIP 18 | PASS 822 ]
    Error: Test failures
    Execution halted
Flavor: [r-devel-linux-x86_64-fedora-gcc](https://www.r-project.org/nosvn/R.check/r-devel-linux-x86_64-fedora-gcc/learnr-00check.html)