Fix failed flaky test, add reindex before test execution

Author: Nazar65

app/code/Magento/SalesRule/Test/Mftf/Test/AdminCreatePercentOfProductPriceTest.xml

@@ -21,6 +21,8 @@
 
         <before>
             <createData entity="_defaultCategory" stepKey="createPreReqCategory"/>
+            <!-- Reindex invalidated indices after product attribute has been created/deleted -->
+            <actionGroup ref="CliRunReindexUsingCronJobsActionGroup" stepKey="reindexInvalidatedIndices"/>
             <actionGroup ref="LoginAsAdmin" stepKey="loginAsAdmin"/>
         </before>