fix(ci): avoid rebuilding email example image (#1400)

Author: lovasoa

examples/sending emails/README.md

@@ -5,7 +5,7 @@ This example sends plain-text email with [`sqlpage.send_mail`](https://sql-page.
 Run the example:
 
 ```sh
-docker compose up --build
+docker compose -f docker-compose.yml -f docker-compose.local.yml up --build
 ```
 
 This builds SQLPage from the current repository checkout before starting the example.

examples/sending emails/docker-compose.local.yml

@@ -0,0 +1,6 @@
+services:
+  web:
+    build:
+      context: ../..
+      args:
+        CARGO_PROFILE: dev

examples/sending emails/docker-compose.yml

@@ -1,10 +1,6 @@
 services:
   web:
     image: lovasoa/sqlpage:main
-    build:
-      context: ../..
-      args:
-        CARGO_PROFILE: dev
     ports:
       - "8080:8080"
     environment: