ci: fix build as sqlalchemy is not supported yet

[juarezr]

This PR has the objective of restricting the maximum supported version of SQLAlchemy.

Changes

1. Added in requirements-database.txt: SQLAlchemy>=1.3.6,<2.0
2. Added in setup.py: SQLAlchemy>=1.3.6,<2.0

For SQLAlchemy >=2.0 check #648.

Checklist

Use this checklist to ensure the quality of pull requests that include new code and/or make changes to existing code.

• Source Code guidelines:
  • Includes unit tests
  • New functions have docstrings with examples that can be run with doctest
  • New functions are included in API docs
  • Docstrings include notes for any changes to API or behavior
  • All changes are documented in docs/changes.rst
• Versioning and history tracking guidelines:
  • Using atomic commits whenever possible
  • Commits are reversible whenever possible
  • There are no incomplete changes in the pull request
  • There is no accidental garbage added to the source code
• Testing guidelines:
  • Tested locally using tox / pytest
  • Rebased to master branch and tested before sending the PR
  • Automated testing passes (see CI)
  • Unit test coverage has not decreased (see Coveralls)
• State of these changes is:
  • Just a proof of concept
  • Work in progress / Further changes needed
  • Ready to review
  • Ready to merge