Don't run rust CI if no rust files have changed (#47)

Author: LegNeato

.github/workflows/rust.yaml

@@ -4,7 +4,15 @@ on:
   push:
     branches:
       - main
+    paths:
+      # Only run when files in blog/*/code change
+      - "blog/*/code/**"
+      - ".github/workflows/rust.yaml"
   pull_request:
+    paths:
+      # Only run when files in blog/*/code change
+      - "blog/*/code/**"
+      - ".github/workflows/rust.yaml"
 
 jobs:
   test: