MAINTENANCE: Automated closing of pull requests.

This commit exists to close the following pull requests on Github:

Closes #8737 (close requested by 'srowen')
Closes #5323 (close requested by 'JoshRosen')
Closes #6148 (close requested by 'JoshRosen')
Closes #7557 (close requested by 'JoshRosen')
Closes #7047 (close requested by 'srowen')
Closes #8713 (close requested by 'marmbrus')
Closes #5834 (close requested by 'srowen')
Closes #7467 (close requested by 'tdas')
Closes #8943 (close requested by 'xiaowen147')
Closes #4434 (close requested by 'JoshRosen')
Closes #8949 (close requested by 'srowen')
Closes #5368 (close requested by 'JoshRosen')
Closes #8186 (close requested by 'marmbrus')
Closes #5147 (close requested by 'JoshRosen')