[fix] Avoid calling getCacheTagsToInvalidateOnUpdate() twice

[squatto]

I'm using an overridden getCacheTagsToInvalidateOnUpdate() to track how many times each tag is invalidated. The way invalidateCache() was originally written calls the getCacheTagsToInvalidateOnUpdate() method twice, resulting in the tags being counted twice for each invalidation. This change simply assigns the tags to a variable and uses the variable instead of calling the method directly.

FWIW, this is what I'm doing to track the tag invalidations. Just a simple array saved to the cache.

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

    $invalidations = Cache::get('cache-invalidations', []);

    foreach ($tags as $tag) {
        $invalidations[$tag] = ($invalidations[$tag] ?? 0) + 1;
    }

    Cache::forever('cache-invalidations', $invalidations);

    return $tags;
}

[codecov]

Codecov Report

Merging #118 (7bd849c) into master (7e77875) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #118   +/-   ##
=======================================
  Coverage   79.34%   79.34%           
=======================================
  Files           4        4           
  Lines         184      184           
=======================================
  Hits          146      146           
  Misses         38       38           

Impacted Files	Coverage Δ
src/FlushQueryCacheObserver.php	52.50% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7e77875...7bd849c. Read the comment docs.