Handle both buildinfo and buildInfo commands

[AlekSi]

The former is sent by the old mongo shell.

[codecov]

Codecov Report

Merging #688 (e365e06) into main (a8751f4) will increase coverage by 0.30%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #688      +/-   ##
==========================================
+ Coverage   63.16%   63.46%   +0.30%     
==========================================
  Files         191      191              
  Lines        7625     7625              
==========================================
+ Hits         4816     4839      +23     
+ Misses       2248     2224      -24     
- Partials      561      562       +1     

Impacted Files	Coverage Δ
internal/handlers/common/msg_listcommands.go	85.71% <ø> (ø)
internal/handlers/common/msg_buildinfo.go	87.50% <0.00%> (+87.50%)	⬆️
internal/handlers/pg/msg_buildinfo.go	100.00% <0.00%> (+100.00%)	⬆️

Flag	Coverage Δ
FerretDB	59.13% <ø> (+0.30%)	⬆️
MongoDB	6.31% <ø> (ø)
integration	59.16% <ø> (+0.30%)	⬆️
unit	23.06% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[w84thesun]

LGTM

[rumyantseva]

LGTM