fix indexing of annual weeks in commit-freq metric

[mpadge]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.43%. Comparing base (2626dfd) to head (4f9834a).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
R/cm-metric-cran-downloads.R	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #95      +/-   ##
==========================================
- Coverage   92.45%   92.43%   -0.02%     
==========================================
  Files          50       50              
  Lines        3392     3397       +5     
==========================================
+ Hits         3136     3140       +4     
- Misses        256      257       +1     

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