make package manual page internal

[maelle]

so that it doesn't turn up in the local nor pkgdown reference index

[codecov]

Codecov Report

Merging #663 (d912eae) into main (f2bb0ef) will increase coverage by 0.00%.
The diff coverage is 78.94%.

❗ Current head d912eae differs from pull request most recent head 4ae3f56. Consider uploading reports for the commit 4ae3f56 to get more accurate results

@@           Coverage Diff           @@
##             main     #663   +/-   ##
=======================================
  Coverage   62.69%   62.70%           
=======================================
  Files          73       73           
  Lines       21536    21571   +35     
=======================================
+ Hits        13502    13526   +24     
- Misses       8034     8045   +11     

Impacted Files	Coverage Δ
R/conversion.R	73.91% <ø> (ø)
R/make.R	91.89% <ø> (ø)
R/structural.properties.R	86.35% <ø> (ø)
R/attributes.R	78.00% <75.00%> (-1.73%)	⬇️
R/interface.R	83.58% <100.00%> (+0.24%)	⬆️
src/rinterface.c	79.24% <100.00%> (ø)

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