Add tbachert/spi to the plugins list [#3501877]

Problem/Motivation

Install is interrupted with Do you trust "tbachert/spi" to execute code and wish to enable it now? (writes "allow-plugins" to composer.json) [y,n,d,?]

Steps to reproduce

1. Spin up a new DrupalPod instance for Drupal 11

Proposed resolution

Adds the plugin to the composer setup script.

Issue fork drupalpod-3501877

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3501877-spi-plugin changes, plain diff MR !11
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