fix: use command -v instead of which in env.sh

Author: Chemaclass

src/env.sh

@@ -147,7 +147,7 @@ TEMP_DIR_PARALLEL_TEST_SUITE="${TMPDIR:-/tmp}/bashunit/parallel/${_OS:-Unknown}/
 TEMP_FILE_PARALLEL_STOP_ON_FAILURE="$TEMP_DIR_PARALLEL_TEST_SUITE/.stop-on-failure"
 TERMINAL_WIDTH="$(env::find_terminal_width)"
 FAILURES_OUTPUT_PATH=$(mktemp)
-CAT="$(which cat)"
+CAT="$(command -v cat)"
 
 if env::is_dev_mode_enabled; then
   internal_log "info" "Dev log enabled" "file:$BASHUNIT_DEV_LOG"