Added explicit YAML import

Author: Joel Collins

poetry.lock

@@ -20,6 +20,10 @@ apispec = "^3.2.0"
 flask-cors = "^3.0.8"
 zeroconf = ">=0.24.5,<0.29.0"
 apispec_webframeworks = "^0.5.2"
+# This may a Poetry bug, but somehow yaml isn't being installed by
+# apispec_webframeworks. This just ensures it gets added.
+# See https://gitlab.com/openflexure/openflexure-microscope-server/-/issues/177
+pyyaml = "^5.3.1"
 
 [tool.poetry.dev-dependencies]
 pytest = "^6.0"