Fix missing `*` in Go Fmt GitHub Actions (#4277)

Looks like one `*` is missing in Go Fmt GitHub Actions
and that causes the Actions not being triggered.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

.github/workflows/go.fmt.yml

@@ -5,7 +5,7 @@ on:
     branches:
       - 'master'
     paths:
-      - '*.go'
+      - '**.go'
 
 jobs:
   fix: