Extend allow_filter in conjunct_test_linter() to allow linting only dplyr::filter() (i.e. qualified)

[MichaelChirico]

Closes #2078

[codecov-commenter]

Codecov Report

Merging #2169 (1b86e1d) into main (8cdf26c) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 1b86e1d differs from pull request most recent head 36f04dc. Consider uploading reports for the commit 36f04dc to get more accurate results

@@           Coverage Diff           @@
##             main    #2169   +/-   ##
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  Coverage   99.64%   99.64%           
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  Files         112      112           
  Lines        5117     5122    +5     
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+ Hits         5099     5104    +5     
  Misses         18       18           

Files Changed	Coverage Δ
R/conjunct_test_linter.R	100.00% <100.00%> (ø)