CI: Exclude vendored sources at cheching if US-ASCII clean

Author: nobu

.github/workflows/check_misc.yml

@@ -40,7 +40,7 @@ jobs:
 
       - name: Check if C-sources are US-ASCII
         run: |
-          grep -r -n --include='*.[chyS]' --include='*.asm' $'[^\t-~]' -- . && exit 1 || :
+          grep -r -n --exclude-dir=vendor --include='*.[chyS]' --include='*.asm' $'[^\t-~]' -- . && exit 1 || :
 
       - name: Check for bash specific substitution in configure.ac
         run: |