Add missing molecule field to cclib TaskDocument

[Andrew-S-Rosen]

Closes #342.

[codecov]

Codecov Report

Merging #343 (96fa4c7) into main (b4a87a3) will decrease coverage by 0.16%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #343      +/-   ##
==========================================
- Coverage   65.73%   65.57%   -0.16%     
==========================================
  Files          72       72              
  Lines        7018     7018              
  Branches      896      896              
==========================================
- Hits         4613     4602      -11     
- Misses       2138     2150      +12     
+ Partials      267      266       -1     

Impacted Files	Coverage Δ
src/atomate2/common/schemas/cclib.py	74.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

[Andrew-S-Rosen]

@utf this is ready to go.