Update swaggerapi/swagger-ui Docker tag to v5.21.0 (#361)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

openapi/Earthfile

@@ -1,7 +1,7 @@
 VERSION 0.8
 
 swagger:
-    FROM swaggerapi/swagger-ui:v5.20.8
+    FROM swaggerapi/swagger-ui:v5.21.0
 
     COPY v1 /usr/share/nginx/html/yaml/
     COPY swagger/fs /