fix: app/backend/requirements.txt to reduce vulnerabilities
fix: app/backend/requirements.txt to reduce vulnerabilities


The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-LXML-1047473
- https://snyk.io/vuln/SNYK-PYTHON-LXML-1047474
bcgov/gwells,bcgov/gwells,bcgov/gwells,bcgov/gwells