tests/exec: Wait after writing to a file before executing it

Otherwise we might get "text file is busy", or worse no error at all.

Hoping .2 seconds is enough here.

tests/checks/exec.fish

@@ -13,6 +13,8 @@ echo "neg failed: $status"
 set -l f (mktemp)
 echo "#!/bin/sh"\r\n"echo foo" > $f
 chmod +x $f
+# Cheesy sleep to avoid "text file is busy"
+sleep 0.2
 $f
 #CHECKERR: Failed to execute process '{{.*}}'. Reason:
 #CHECKERR: The file uses windows line endings (\r\n). Run dos2unix or similar to fix it.