Update Synapse workflow for PR

[NeilGorman104]

Description

Updates the Synapse Workflow to run on Pull Requests from the Synapse Branch

Uses the following function to only run if the PR is from the "synapse" branch:

  build:
    runs-on: ubuntu-latest

    steps:
    - name: Check source branch name
      run: |
        if [[ "${{ github.head_ref }}" != "synapse" ]]; then
          exit 1
        fi

Related Issues

Resolves issue with Synapse tests not running in the dlt repo from Synapse destination fork

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