Update WordPress Importer version used in tests

[jorbin]

Version 0.6.4 of the Importer contains some compatability issues with PHP 7.4 that are fixed in the trunk version of the importer. A new release of the importer needs to be made and the travis config updated to pull in this new version.

[jorbin]

@ocean90 said in slack that he was going to look into the Importer plugin and see about releasing a new version. If he can't maybe bocean901 can.

[jorbin]

Assigning to @ocean90, who is welcome to bounce it back after the update is out.

[desrosj]

@ocean90 Do we have an ETA for the new importer release?

[ocean90]

There's no ETA. Feel free to switch the travis config to checkout ​rev 2170172 if you think this is blocking anything.

[jorbin]

In 46542:

Build/Test tools use Trunk revision 2170172 of importer

Update Travis configuration to temporarily use trunk for the importer in order for PHP 7.4 tests to pass. When the new version is released, this will be updated to point to that tag.

See: #48231

[jorbin]

As a blessed task that won't touch the actual released code, I think that this can roll into RC.

[johnbillion]

Marking this as fixed for 5.3. If and when the plugin gets a new stable release we can update to that in another ticket.