MNT: Move to Github Actions dynamic matrix

[chrispenny]

Blocker at the moment is that PostgreSQL tests are failing:
https://github.com/silverstripe/silverstripe-populate/actions/runs/3146840126/jobs/5115740952

[emteknetnz]

The github action logs will be scrubbed after a time period (90 days I think), so I'll post the failure here for future generations:

1) DNADesign\Populate\Tests\PopulateFactoryTest::testVersionedObjects
SilverStripe\ORM\Connect\DatabaseException: Couldn't run query:

SELECT DISTINCT count(DISTINCT "PopulateFactoryTestVersionedObject"."ID") AS "Count"

FROM "PopulateFactoryTestVersionedObject"

WHERE (Title = 'Version Foo')

ERROR:  column "title" does not exist
LINE 3:  WHERE (Title = 'Version Foo')
                ^
HINT:  Perhaps you meant to reference the column "PopulateFactoryTestVersionedObject.Title".

/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/Connect/DBConnector.php:64
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/postgresql/code/PostgreSQLConnector.php:234
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/Connect/Database.php:185
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/Connect/Database.php:258
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/Connect/Database.php:183
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/DB.php:445
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/Queries/SQLExpression.php:115
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/Queries/SQLSelect.php:646
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/DataQuery.php:458
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/DataList.php:883
/home/runner/work/silverstripe-populate/silverstripe-populate/code/PopulateFactory.php:107
/home/runner/work/silverstripe-populate/silverstripe-populate/tests/php/PopulateFactoryTest.php:52
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/bin/phpunit:123

2) DNADesign\Populate\Tests\PopulateFactoryTest::testCreateObjectPopulateMergeWhen
SilverStripe\ORM\Connect\DatabaseException: Couldn't run query:

SELECT DISTINCT count(DISTINCT "PopulateFactoryTestObject"."ID") AS "Count"

FROM "PopulateFactoryTestObject"

WHERE (Title = 'Foo')

ERROR:  column "title" does not exist
LINE 3:  WHERE (Title = 'Foo')
                ^
HINT:  Perhaps you meant to reference the column "PopulateFactoryTestObject.Title".

/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/Connect/DBConnector.php:64
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/postgresql/code/PostgreSQLConnector.php:234
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/Connect/Database.php:185
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/Connect/Database.php:258
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/Connect/Database.php:183
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/DB.php:445
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/Queries/SQLExpression.php:115
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/Queries/SQLSelect.php:646
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/DataQuery.php:458
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/silverstripe/framework/src/ORM/DataList.php:883
/home/runner/work/silverstripe-populate/silverstripe-populate/code/PopulateFactory.php:107
/home/runner/work/silverstripe-populate/silverstripe-populate/tests/php/PopulateFactoryTest.php:89
/home/runner/work/silverstripe-populate/silverstripe-populate/vendor/bin/phpunit:123