Add SQLite to test matrix

[Copilot]

Adds SQLite testing to the automated test matrix to provide visibility into SQLite compatibility across WP-CLI packages.

Changes

• Added dbtype matrix dimension (default: mysql)
• Added SQLite test entries for 6 packages (wp-cli-bundle, wp-cli, cache-command, config-command, core-command, entity-command) on PHP 8.5 + WP trunk
• Added pdo_sqlite PHP extension and WP_CLI_TEST_DBTYPE environment variable
• Skip MySQL setup and database preparation when dbtype == 'sqlite'
• SQLite tests marked with continue-on-error: true to prevent CI pipeline blocking
• Updated job names to display database type

Example test configuration:

- php: '8.5'
  wp: 'trunk'
  dbtype: 'sqlite'
  use-phar: false
  test-package: 'core-command'

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add SQLite to test matrix</issue_title>
<issue_description>All individual packages run tests against SQLite already and for most of them they already pass.

Adding SQLite to the test matrix in this repo would make it easier to see SQLite compatibility at a glance.</issue_description>

<agent_instructions>SQLite tests should be allowed to fail</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@danielbachhuber Seems fine 👍

• Fixes Add SQLite to test matrix #39

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