Fix branch info for docker build

[bmuskalla]

Why are these changes needed?

Running the existing commands leads to the following error as docker build by default uses the master branch.

❯ docker build -f .devcontainer/full/Dockerfile -t autogen_full_img https://github.com/microsoft/autogen.git

unable to prepare context: unable to 'git clone' to temporary context directory: error fetching: fatal: couldn't find remote ref master
: exit status 128

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 37.30%. Comparing base (c75655a) to head (d467007).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1935   +/-   ##
=======================================
  Coverage   37.30%   37.30%           
=======================================
  Files          64       64           
  Lines        6910     6910           
  Branches     1519     1519           
=======================================
  Hits         2578     2578           
  Misses       4109     4109           
  Partials      223      223           

Flag	Coverage Δ
unittests	37.30% <ø> (ø)

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

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

[ekzhu]

Thanks for the PR. Though how come I don't have this issue?