Add const keyword to CrossSection::Compose parameter

[tomasf]

Add a missing const to the crossSections parameter ofCrossSection::Compose.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.58%. Comparing base (1b3dbc2) to head (ba69f68).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1129   +/-   ##
=======================================
  Coverage   91.58%   91.58%           
=======================================
  Files          30       30           
  Lines        5915     5915           
=======================================
  Hits         5417     5417           
  Misses        498      498           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[elalish]

Thanks!