test: Limit tox execution

Only run tox when code changes.

Author: jongracecox

.github/workflows/tox.yaml

@@ -4,9 +4,17 @@ on:
   push:
     branches:
       - master
+    paths:
+      - 'anybadge/**'
+      - 'tests/**'
+      - '.github/workflows/**'
   pull_request:
     branches:
       - master
+    paths:
+      - 'anybadge/**'
+      - 'tests/**'
+      - '.github/workflows/**'
 
 jobs:
   test: