Refactor parts initialization inside try block

Moved the initialization of the `parts` variable, which splits the `_idToken` string, inside the `try` block. Removed the previous check for exactly three elements in the `parts` array and the default return value if the check failed.

Author: tg123

src/KubernetesClient/Authentication/OidcTokenProvider.cs

@@ -37,14 +37,9 @@ public async Task<AuthenticationHeaderValue> GetAuthenticationHeaderAsync(Cancel
 
         private DateTimeOffset GetExpiryFromToken()
         {
-            var parts = _idToken.Split('.');
-            if (parts.Length != 3)
-            {
-                return default;
-            }
-
             try
             {
+                var parts = _idToken.Split('.');
                 var payload = parts[1];
                 var jsonBytes = Base64UrlDecode(payload);
                 var json = Encoding.UTF8.GetString(jsonBytes);