Add phpunit 9 support (to allow testing on PHP 8)

[ADmad]

No description provided.

[othercorey]

3) Cake\Test\TestCase\Database\Type\DateTypeTest::testMarshal with data set #9 ('2014-02-14', Cake\Chronos\Date Object (...))
Failed asserting that two DateTime objects are equal.
--- Expected
+++ Actual
@@ @@
-2014-02-14T00:00:00.000000+0000
+2014-02-14T07:42:50.000000+0000

This looks like a fun failure.

[ADmad]

Errors on PHP 8:

• Function openssl_free_key() is deprecated

  I couldn't find any info regarding this. I tried replacing it with openssl_pkey_free() which is apparently it's alias but that function too gives deprecation error. So nothing sure if there's some alternative or we just need to drop it's usage for PHP 8.

• Function libxml_disable_entity_loader() is deprecated

  Based on Bump libxml version, deprecate libxml_disable_entity_loader() php/php-src#5867 and Fix deprecated libxml_disable_entity_loader symfony/symfony#37763 loading external entities is disabled by default since v2.9. So the solution is to check libxml version and use the method only for < 2.9. For higher versions use LIBXML_NOENT flag instead of enable.

• PHP version constraint for https://github.com/auraphp/Aura.Intl/blob/3.x/composer.json#L23 would have to be bumped. Aura project seem to be dead. I'll make a PR and see how it goes.

[ADmad]

Last commit to Aura.Intl was on Jan 20, 2017. Even running it's test suite with a recent phpunit version would be non trivial. I think it would be better if we just copy the classes we need and move on.

[othercorey]

I couldn't find any info regarding this. I tried replacing it with openssl_pkey_free() which is apparently it's alias but that function too gives deprecation error. So nothing sure if there's some alternative or we just need to drop it's usage for PHP 8.

The openssl_pkey_free() function is deprecated and no longer has an effect,
instead the OpenSSLAsymmetricKey instance is automatically destroyed if it is no
longer referenced.

https://github.com/php/php-src/blob/master/UPGRADING#L397

[ADmad]

https://github.com/php/php-src/blob/master/UPGRADING#L397

Good, so just need to wrap the call in a PHP version check.

[othercorey]

We can commit this with failures allowed so people can test fixes or will have to wait work on them here.

[ADmad]

Once #14885 is merged and forwarded to 4.next the build on PHP 8 will start passing so there's no need to modify the travis matrix.

[othercorey]

Looks ok to me.

[ADmad]

This is ready to merge now.

The only remaining failure for DateTimeType marshalling needs a fix in Chronos (which isn't an easy fix) and dealing with the warnings for usage of at() for mocks will take significant amount of effort given the number of usages. Perhaps this would be a good time to start switching to Mockery instead.