Pin python dependency versions

app/requirements.txt

-django-guardian
-pgpy
-fontawesome-free
-django-crispy-forms
-django_compressor
-django-libsass
-psycopg2
-
+django~=3.1.7
+django-guardian~=2.30
+pgpy~=0.5.3
+fontawesome-free~=5.15.3
+django-crispy-forms~=1.11.2
+django_compressor~=2.4
+django-libsass~=0.20.1
+psycopg2~=2.8.6