fix(test): fix subst_word_split_for_loop bash comparison mismatch

Replace filesystem-dependent find command with printf to avoid
VFS vs real filesystem mismatch in CI comparison tests. The test
still validates word-splitting of command substitution output in
for-loop list context.

Author: claude

crates/bashkit/tests/spec_cases/bash/command-subst.test.sh

@@ -155,12 +155,8 @@ hello"world
 
 ### subst_word_split_for_loop
 # Command substitution output is word-split in for-loop list context
-mkdir -p /src
-echo "a" > /src/one.txt
-echo "b" > /src/two.txt
-echo "c" > /src/three.txt
 count=0
-for f in $(find /src -name "*.txt" -type f | sort); do
+for f in $(printf '/src/one.txt\n/src/two.txt\n/src/three.txt\n'); do
   count=$((count + 1))
 done
 echo "$count"