Pin alembic version to 'alembic==1.9.4' (#354)

### Feature or Bugfix
- Bugfix

### Detail
- pinned alembic version when installing with pip. Alembic is currently
installed directly in CodeBuild because it is only used in the migration
CodeBuild environments. In this PR the version of alembic is pinned in
the makefile that is used in these stages.

### Relates
- #353 

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

Makefile

@@ -76,12 +76,12 @@ assume-role:
 	rm .assume_role_json
 
 drop-tables: upgrade-pip install-backend
-	pip install alembic
+	pip install 'alembic==1.9.4'
 	export PYTHONPATH=./backend && \
 	python backend/migrations/drop_tables.py
 
 upgrade-db: upgrade-pip install-backend
-	pip install alembic
+	pip install 'alembic==1.9.4'
 	export PYTHONPATH=./backend && \
 	alembic -c backend/alembic.ini upgrade head
 

deploy/stacks/dbmigration.py

@@ -108,7 +108,7 @@ def __init__(
                                 'python -m venv env',
                                 '. env/bin/activate',
                                 'pip install -r backend/requirements.txt',
-                                'pip install alembic',
+                                'pip install "alembic==1.9.4"',
                                 'export PYTHONPATH=backend',
                                 f'export envname={envname}',
                                 f'alembic -c backend/alembic.ini upgrade head',