fix: Don't run tests that invoke re2 by default

[krlmlr]

Closes #121.

[krlmlr]

Also checking with rhub2 in https://github.com/duckdb/duckdb-r/actions/runs/8410717718.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.53%. Comparing base (5257514) to head (572feb4).

❗ Current head 572feb4 differs from pull request most recent head 6bb56e4. Consider uploading reports for the commit 6bb56e4 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #127      +/-   ##
==========================================
- Coverage   86.28%   84.53%   -1.76%     
==========================================
  Files         107      107              
  Lines        3712     3712              
==========================================
- Hits         3203     3138      -65     
- Misses        509      574      +65     

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[krlmlr]

rhub2: https://github.com/duckdb/duckdb-r/actions/runs/8410799197

[krlmlr]

valgrind is green, yay!