chore: se extrae image a Dockerfile

Dockerfile

@@ -0,0 +1 @@
+FROM python:3.9-bullseye

compose.test.yml

@@ -3,7 +3,8 @@ include:
   - compose.base.yml
 services:
   app.dev:
-    image: python:3.9
+    build:
+      context: .
     environment:
       - DB_CACHE=/tmp
       - DB_NAME=trytontest

compose.yml

@@ -3,7 +3,8 @@ include:
   - compose.base.yml
 services:
   app.dev:
-    image: python:3.9
+    build:
+      context: .
     depends_on:
       - db.dev
     command: bash .dev/run.sh