undeclared_variables() stuck with for loop ({% for ... in ... %})

[gemhtcr]

Description

minijinja undeclared_variables() stucks when there is a variable in for loop

[What happened]
The running code stuck and never exited

Reproduction steps

// main.rs
// Running the code below
fn main() {
    let mut env = minijinja::Environment::new();
    env.add_template("my_test", {
        r#"
            {% for item in content.products.items() %}
              {{ foo.bar }}                          
              {{ item.name }}  // remove this line and it will run to exit
            {% endfor %}
        "#
    })
    .unwrap();
    let tpl = env.get_template("my_test").unwrap();
    println!("check point 1");
    let ret = tpl.undeclared_variables(true);     <-- stuck here
    println!("check point 2, ret={:?}", ret);    <-- never see this
}

# Cargo.toml
[package]
name = "undeclared_variables_stuck_issue"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
minijinja = "1.0.17"

Additional helpful information:

• Version of minijinja:

1.0.17

• Version of rustc:

rustc 1.76.0 (07dca489a 2024-02-04)

• Operating system and version:

ProductName:            macOS
ProductVersion:         14.2.1
BuildVersion:           23C71

• If set nested param to false, it's able to run to exit

What did you expect

When running the code above, I expect to see

check point 1
check point 2, ret={"foo.bar", "content.products.items"}
# Note that the output didn't have `item.name` 
# cause it's a declared variable in for loop

[What you think should have happened]
The cpu is high (20 % v.s 5%) all time when running the code above, I guess it might enter an infinite cyclic loop