Added tbachert/spi to config.allow-plugins of composer.json.

[AlexSkrypnyk]

Similar to #685

Drupal core aded dependency on tbachert/spi and it is now needs to be added to config.allow-plugins of composer.json.

$ composer why -r tbachert/spi
drupal-composer/drupal-project 11.x-dev requires (for development) drupal/core-dev (^11)             
drupal/core-dev                11.0.5   requires                   open-telemetry/exporter-otlp (^1) 
drupal/core-dev                11.0.5   requires                   open-telemetry/sdk (^1)           
open-telemetry/api             1.1.0    conflicts                  open-telemetry/sdk (<=1.0.8)      
open-telemetry/exporter-otlp   1.1.0    requires                   open-telemetry/sdk (^1.0)         
open-telemetry/sdk             1.1.0    requires                   tbachert/spi (^1.0.1)