Install shipengine package in CI before running tests

Add 'pip install -e .' to install the shipengine package itself
before running tests. This fixes ModuleNotFoundError.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: semarj

.github/workflows/CI.yml

@@ -40,6 +40,7 @@ jobs:
         python -m pip install --upgrade pip
         python -m pip install flake8 pytest tox pytest-cov coverage
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+        pip install -e .
     - name: Lint with flake8
       run: |
         # stop the build if there are Python syntax errors or undefined names
@@ -68,6 +69,7 @@ jobs:
           python -m pip install --upgrade pip
           python -m pip install tox pytest pytest-cov coverage responses
           if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+          pip install -e .
 
       - name: Pytest
         run: |