Fix copilot-setup-steps: replace reusable workflow with direct steps

[m7pr]

This PR fixes the GitHub Copilot setup workflow by replacing the reusable workflow call with direct steps, as required by GitHub Copilot's limitations for copilot-setup-steps jobs.

Changes:

• Removed uses: insightsengineering/r.pkg.template/.github/workflows/copilot-setup-steps.yaml@main
• Added direct steps for checkout, R setup, and dependency installation
• Uses actions with uses: (which is allowed) instead of reusable workflows (which are not)

This resolves the error: 'Calling a reusable workflow with the uses: keyword is not supported in copilot-setup-steps jobs.'

[github-actions]

Code Coverage Summary

Filename                     Stmts    Miss  Cover    Missing
-------------------------  -------  ------  -------  -------------------
R/cdisc_data.R                   1       0  100.00%
R/deprecated.R                  18       0  100.00%
R/dummy_function.R               2       2  0.00%    15-16
R/formatters_var_labels.R       61       0  100.00%
R/join_key.R                    38       0  100.00%
R/join_keys-c.R                 12       0  100.00%
R/join_keys-extract.R          128       0  100.00%
R/join_keys-names.R             15       0  100.00%
R/join_keys-parents.R           30       0  100.00%
R/join_keys-print.R             45       0  100.00%
R/join_keys-utils.R             73       3  95.89%   35-38
R/join_keys.R                   21       0  100.00%
R/teal_data-class.R             36       6  83.33%   50-52, 59, 104-105
R/teal_data-constructor.R       11       2  81.82%   48, 51
R/teal_data-extract.R            3       0  100.00%
R/teal_data-get_code.R          13       8  38.46%   114-120, 124
R/teal_data-names.R              8       1  87.50%   42
R/teal_data-show.R               5       5  0.00%    14-20
R/topological_sort.R            32       0  100.00%
R/verify.R                      42      11  73.81%   67, 97-101, 104-108
TOTAL                          594      38  93.60%

Diff against main

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

Results for commit: 2328ed1

Minimum allowed coverage is 80%

♻️ This comment has been updated with latest results

[github-actions]

Unit Tests Summary

  1 files   15 suites   2s ⏱️
163 tests 163 ✅ 0 💤 0 ❌
218 runs  218 ✅ 0 💤 0 ❌

Results for commit 2328ed1.

♻️ This comment has been updated with latest results.