codesigning: error when parsing smartcard xml

### Error

The codesigning tool is throwing an error when running an iOS app on Mac devices with an identity provider (IdP).

The error returned is this:
```log
ValueError: time data 'N/A' does not match format '%Y-%m-%d %H:%M:%S %z'
```

### Cause

The error happens because these devices include a key without an expiration date in their keychain, so the following command

```bash
system_profiler SPSmartCardsDataType -xml
```

Returns an expiration with the value 'N/A':

```xml

#01
Kind: private ECDSA 256-bit, Certificate: no, Usage: Derive Decrypt Unwrap
Valid from: N/A to: N/A, SSL trust: N/A, X509 trust: N/A

_name
com.apple.platformsso:BBBBBBBBBBB

```

And when the python script tries to parse it, it simply fails:

```py
expiry_date = re.search(r"(?<=to:)(.*?)(?=,)", data, re.DOTALL).group().strip()
expiry_date = datetime.datetime.strptime(expiry_date, "%Y-%m-%d %H:%M:%S %z")
```

Start from the Python parsing snippet in the issue and trace the code that reads the smartcard XML output. Verify handling for an expiration value of 'N/A' while preserving normal date parsing, then confirm the codesigning command no longer raises this error for the shown keychain entry.

Written by the indexing model from the issue text.