CI: run the migrations on MySQL, MariaDB and PostgreSQL

[njoubert-cleverage]

Fixes #129

Changes

• test.yml: new migrations job, matrix MySQL 8.4 / MariaDB 11.4 / PostgreSQL 17 × DBAL 3 (PHP 8.4, Symfony 7.4) / DBAL 4 (PHP 8.5, highest):
  1. doctrine:migrations:migrate
  2. doctrine:schema:validate: the schema created by the migrations matches the mapping
  3. doctrine:migrations:migrate first: all the down() methods
  4. doctrine:migrations:migrate and doctrine:schema:validate again
• tests/App/bin/console: console of the test application
• tests/App/config/packages.yaml: database URL overridable with DATABASE_URL, SQLite by default (the functional tests are unchanged)

DBAL 3 on PostgreSQL

doctrine:schema:validate is skipped: DBAL 3 does not read the identity columns created by the migrations (#99), it expects sequences (with AUTO: CREATE SEQUENCE ...; with the identity_generation_preferences of the Symfony recipe: CREATE SEQUENCE + ALTER ... SET DEFAULT nextval(...)), so the schema is always reported as out of sync. Inserts work (checked with process executions: ids generated), the ORM uses the sequence created by PostgreSQL for the identity column (<table>_id_seq). The migrations themselves (up, down, up) are run.

Checks (locally, same sequence, throwaway containers)

	MySQL 8.4	MariaDB 11	PostgreSQL 17
DBAL 4.5	OK	OK	OK
DBAL 3.10 (Symfony 7.4)	OK	OK	OK (without schema:validate)

• Without the Version20261008120000 migration (Cosmetic cleanup: (DC2Type) column comments, UiOptions PHPDoc #127), doctrine:schema:validate fails (exit 2) on MySQL: the job would have detected it.
• serverVersion is set in the URLs (with DBAL 4 on PostgreSQL, without it: Invalid platform version "").
• actionlint OK; PHPStan, PHP-CS-Fixer, Rector OK; PHPUnit 292 tests OK.

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