Change branch name used in metadata update github action

[jaydeluca]

Last night's run failed with:

Run BRANCH_NAME="metadata-update-main"
[metadata-update-main b2dd798] chore: update instrumentation list [automated]
 1 file changed, 8 insertions(+)
remote: error: GH013: Repository rule violations found for refs/heads/metadata-update-main.        
remote: Review all repository rules at https://github.com/open-telemetry/opentelemetry-java-instrumentation/rules?ref=refs%2Fheads%2Fmetadata-update-main        
remote: 
remote: - Required status check "EasyCLA" is expected.        
remote: 
To https://github.com/open-telemetry/opentelemetry-java-instrumentation
 ! [remote rejected] metadata-update-main -> metadata-update-main (push declined due to repository rule violations)
error: failed to push some refs to 'https://github.com/open-telemetry/opentelemetry-java-instrumentation'
Error: Process completed with exit code 1.

Added otelbot/ to the branch name to follow the pattern used elsewhere to bypass this check