we really shouldn't warn on these errors, action author can decide what to do (#837)

src/internal-hash-files.ts

@@ -36,7 +36,7 @@ export async function hashFiles(globber: Globber): Promise<string> {
     core.debug(`Found ${count} files to hash.`)
     return result.digest('hex')
   } else {
-    core.warning(`No matches found for glob`)
+    core.debug(`No matches found for glob`)
     return ''
   }
 }