fix some new chrono warnings (#10384)

# Description

This PR cleans up some warnings on the latest chrono dependency.

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->

# Tests + Formatting
<!--
Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used` to
check that you're using the standard code style
- `cargo test --workspace` to check that all tests pass (on Windows make
sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- `cargo run -- -c "use std testing; testing run-tests --path
crates/nu-std"` to run the tests for the standard library

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```
-->

# After Submitting
<!-- If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.
-->

crates/nu-cmd-dataframe/src/dataframe/values/nu_dataframe/conversion.rs

@@ -269,7 +269,7 @@ pub fn from_parsed_columns(column_values: ColumnMap) -> Result<NuDataFrame, Shel
                 InputType::Date => {
                     let it = column.values.iter().map(|v| {
                         if let Value::Date { val, .. } = &v {
-                            Some(val.timestamp_nanos())
+                            Some(val.timestamp_nanos_opt().unwrap_or_default())
                         } else {
                             None
                         }
@@ -413,7 +413,7 @@ fn input_type_list_to_series(
 
                 let it = v.as_list()?.iter().map(|v| {
                     if let Value::Date { val, .. } = &v {
-                        Some(val.timestamp_nanos())
+                        Some(val.timestamp_nanos_opt().unwrap_or_default())
                     } else {
                         None
                     }