Bump idna from 3.6 to 3.7 in /server

Bumps [idna](https://github.com/kjd/idna) from 3.6 to 3.7.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.rst)
- [Commits](kjd/idna@v3.6...v3.7)

---
updated-dependencies:
- dependency-name: idna
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

server/requirements.txt

@@ -126,7 +126,7 @@ httplib2==0.22.0
     # via oauth2client
 icalendar==4.0.9
     # via superdesk-planning
-idna==3.6
+idna==3.7
     # via requests
 itsdangerous==1.1.0
     # via
@@ -156,6 +156,7 @@ lxml==4.6.5
     # via
     #   draftjs-exporter
     #   superdesk-core
+    #   xmlsec
 markupsafe==2.0.1
     # via
     #   jinja2
@@ -287,3 +288,5 @@ werkzeug==1.0.1
     #   superdesk-core
 wrapt==1.14.1
     # via elastic-apm
+xmlsec==1.3.13
+    # via superdesk-core