Fix test coverage for 7.x-2.x branch on PHP 8.1 (blocked by Migrate)

Most of the PHP 8.1 bugs have been fixed, this is the remaining one:

Date.DateMigrateTestCase
✗	
include_once
exception: [Deprecated] Line 15 of sites/all/modules/migrate/includes/source.inc:
Return type of MigrateSource::current() should either be compatible with Iterator::current(): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

exception: [Deprecated] Line 15 of sites/all/modules/migrate/includes/source.inc:
Return type of MigrateSource::next() should either be compatible with Iterator::next(): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

exception: [Deprecated] Line 15 of sites/all/modules/migrate/includes/source.inc:
Return type of MigrateSource::key() should either be compatible with Iterator::key(): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

exception: [Deprecated] Line 15 of sites/all/modules/migrate/includes/source.inc:
Return type of MigrateSource::valid() should either be compatible with Iterator::valid(): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

exception: [Deprecated] Line 15 of sites/all/modules/migrate/includes/source.inc:
Return type of MigrateSource::rewind() should either be compatible with Iterator::rewind(): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

exception: [Deprecated] Line 864 of sites/all/modules/migrate/plugins/sources/xml.inc:
Return type of MigrateXMLReader::current() should either be compatible with Iterator::current(): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

exception: [Deprecated] Line 864 of sites/all/modules/migrate/plugins/sources/xml.inc:
Return type of MigrateXMLReader::next() should either be compatible with Iterator::next(): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

exception: [Deprecated] Line 864 of sites/all/modules/migrate/plugins/sources/xml.inc:
Return type of MigrateXMLReader::key() should either be compatible with Iterator::key(): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

exception: [Deprecated] Line 864 of sites/all/modules/migrate/plugins/sources/xml.inc:
Return type of MigrateXMLReader::valid() should either be compatible with Iterator::valid(): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

exception: [Deprecated] Line 864 of sites/all/modules/migrate/plugins/sources/xml.inc:
Return type of MigrateXMLReader::rewind() should either be compatible with Iterator::rewind(): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

exception: [Deprecated] Line 3567 of includes/bootstrap.inc:
Return type of MigrateSQLMap::current() should either be compatible with Iterator::current(): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

exception: [Deprecated] Line 3567 of includes/bootstrap.inc:
Return type of MigrateSQLMap::next() should either be compatible with Iterator::next(): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

exception: [Deprecated] Line 3567 of includes/bootstrap.inc:
Return type of MigrateSQLMap::key() should either be compatible with Iterator::key(): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

exception: [Deprecated] Line 3567 of includes/bootstrap.inc:
Return type of MigrateSQLMap::valid() should either be compatible with Iterator::valid(): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

exception: [Deprecated] Line 3567 of includes/bootstrap.inc:
Return type of MigrateSQLMap::rewind() should either be compatible with Iterator::rewind(): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

This is blocked on the Migrate module: #3301821