On update, cache flush bug

[shixue]

The cause of this bug (issues #97) :
QueryCacheable:

public function getCacheTagsToInvalidateOnUpdate($relation = null, $pivotedModels = null): array
{
    return $this->getCacheBaseTags();
}

Example:

User::cacheTags(['user:29'])->find(29);
$userId = 28;
$model = User::cacheTags(['user:' . $userId])->find($userId);
//...
$model->update(['ip' => $ip]);

When specifying the cacheTags getCacheTagsToInvalidateOnUpdate() method should return it.
All that is returned so far is getCacheBaseTags(), the cached updated tags are static::class, not the specified tags.
Just like the flushQueryCache() method, use it if tags are specified, otherwise use the getCacheBaseTags() method.

[shixue]

Tags can be added to the Model after the queried.
getCacheTagsToInvalidateOnUpdate() method to obtain the Model of the specified Tags, if the Model exists to specify Tags.

[kevinlau-drewberry]

@shixue would you mind explaining how to add tags after a query is made?