[fix]: fix shell scripts in aws_ami (#32824)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Bug Fixes**
- Updated the loop condition in the URL encoding functionality for
improved reliability.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

deploy/aws_ami/first-time-setup.sh

@@ -48,7 +48,7 @@ urlencode() {
     LC_COLLATE=C
 
     local length="${#1}"
-    for (( i = 0; i < length; i++ )); do
+    for (( i = 0; i < $length; i++ )); do
         local c="${1:i:1}"
         case $c in
             [a-zA-Z0-9.~_-]) printf "$c" ;;