fix: src/emailservice/requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-JINJA2-6809379

src/emailservice/requirements.txt

@@ -20,7 +20,7 @@ grpcio-health-checking==1.30.0  # via -r requirements.in
 grpcio==1.36.1            # via -r requirements.in, google-api-core, grpcio-health-checking, opentelemetry-instrumentation-grpc
 httplib2==0.19.0          # via -r requirements.in, google-api-python-client, google-auth-httplib2
 idna==2.10                # via requests
-jinja2==2.11.3            # via -r requirements.in
+jinja2==3.1.4            # via -r requirements.in
 markupsafe==1.1.1         # via jinja2
 opentelemetry-api==0.17b0  # via -r requirements.in, opentelemetry-exporter-google-cloud, opentelemetry-instrumentation, opentelemetry-instrumentation-grpc, opentelemetry-sdk
 opentelemetry-exporter-google-cloud==0.17b0  # via -r requirements.in