expr: Test handling '$' at the end of an alternative pattern

Author: frendsick

tests/by-util/test_expr.rs

@@ -290,6 +290,10 @@ fn test_regex() {
         .args(&["a$b", ":", "a\\$b"])
         .succeeds()
         .stdout_only("3\n");
+    new_ucmd!()
+        .args(&["a", ":", "a$\\|b"])
+        .succeeds()
+        .stdout_only("1\n");
     new_ucmd!()
         .args(&["abc", ":", "^abc"])
         .succeeds()