update testthat version

[donyunardi]

Fixes #219

We need to bump up testthat version because we're using testthat::it function in unit tests.

This function was introduced in 3.1.8:
https://github.com/r-lib/testthat/blob/v3.1.8/R/describe.R#L89

[github-actions]

Code Coverage Summary

Filename                         Stmts    Miss  Cover    Missing
-----------------------------  -------  ------  -------  ---------
R/qenv-concat.R                     10       0  100.00%
R/qenv-constructor.R                16      13  18.75%   54-93
R/qenv-eval_code.R                  52       2  96.15%   100, 109
R/qenv-get_code.R                   28       0  100.00%
R/qenv-get_env.R                     3       3  0.00%    23-31
R/qenv-get_var.R                    19       0  100.00%
R/qenv-get_warnings.R               24       0  100.00%
R/qenv-join.R                       46       0  100.00%
R/qenv-show.R                        1       1  0.00%    19
R/qenv-within.R                      8       0  100.00%
R/utils-get_code_dependency.R      191       1  99.48%   283
R/utils.R                           10       0  100.00%
TOTAL                              408      20  95.10%

Diff against main

Filename      Stmts    Miss  Cover
----------  -------  ------  --------
TOTAL             0       0  +100.00%

Results for commit: 6b0072f

Minimum allowed coverage is 80%

♻️ This comment has been updated with latest results

[github-actions]

Unit Tests Summary

  1 files    9 suites   1s ⏱️
109 tests 107 ✅ 2 💤 0 ❌
198 runs  196 ✅ 2 💤 0 ❌

Results for commit 6b0072f.

♻️ This comment has been updated with latest results.

[donyunardi]

Scheduled pipelines passed:
https://github.com/insightsengineering/teal.code/actions/runs/11567017417

[gogonzo]

Good catch 👍