chore: Fix tests when dplyr is missing

[krlmlr]

.

[codecov-commenter]

Codecov Report

Merging #29 (bbd195f) into main (4625214) will not change coverage.
Report is 2 commits behind head on main.
The diff coverage is n/a.

❗ Current head bbd195f differs from pull request most recent head c05bbf5. Consider uploading reports for the commit c05bbf5 to get more accurate results

@@           Coverage Diff           @@
##             main      #29   +/-   ##
=======================================
  Coverage   85.75%   85.75%           
=======================================
  Files         106      106           
  Lines        3601     3601           
=======================================
  Hits         3088     3088           
  Misses        513      513           

Files	Coverage Δ
R/backend-dbplyr__duckdb_connection.R	92.63% <ø> (ø)

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