fix(dev): Don't crash on exports with GitHub intentionally disabled

[nellh]

This exception was added to catch this misconfiguration but it means this can't be disabled when intended. Skip creating this sibling when the remote GitHub remote is disabled.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 42.97%. Comparing base (25ee4ad) to head (3ea1777).
⚠️ Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
services/datalad/datalad_service/common/github.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3642      +/-   ##
==========================================
- Coverage   42.97%   42.97%   -0.01%     
==========================================
  Files         635      635              
  Lines       33808    33807       -1     
  Branches     1515     1515              
==========================================
- Hits        14530    14529       -1     
  Misses      19139    19139              
  Partials      139      139              

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.