fix: use portable arithmetic syntax for bash 5.x

((VAR++)) returns exit code 1 when VAR=0 in newer bash versions,
causing failures with set -e. Use VAR=$((VAR + 1)) instead.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Test User

.github/workflows/test.yml

@@ -31,4 +31,4 @@ jobs:
           git config --global user.name "Test User"
 
       - name: Run tests
-        run: bash -x tests/test_runner.sh
+        run: bash tests/test_runner.sh

tests/test_runner.sh

@@ -131,7 +131,7 @@ run_test() {
   local test_name="$1"
   local test_func="$2"
 
-  ((TESTS_RUN++))
+  TESTS_RUN=$((TESTS_RUN + 1))
 
   # Setup fresh environment for each test
   setup_test_env
@@ -141,10 +141,10 @@ run_test() {
   # Run test in subshell to catch failures
   if (set -e; $test_func) 2>/dev/null; then
     echo "${GREEN}PASS${RESET}"
-    ((TESTS_PASSED++))
+    TESTS_PASSED=$((TESTS_PASSED + 1))
   else
     echo "${RED}FAIL${RESET}"
-    ((TESTS_FAILED++))
+    TESTS_FAILED=$((TESTS_FAILED + 1))
   fi
 
   # Cleanup