build(workflows): add each workflow to its own trigger conditions

For each workflow, add its path to its own trigger conditions so that it automatically re-triggers for testing purposes whenever it is changed.

PR: #443

.github/workflows/build.yml

@@ -1,9 +1,11 @@
 on:
   push:
     paths:
+      - ".github/workflows/build.yml"
       - "app/**"
   pull_request:
     paths:
+      - ".github/workflows/build.yml"
       - "app/**"
 
 name: Build