Add national to the list of extension-compatible formats #548

Job	Run time
Python 3.8 / dj32	39s
Python 3.8 / dj41	39s
Python 3.8 / dj42	49s
Python 3.9 / dj32	38s
Python 3.9 / dj41	36s
Python 3.9 / dj42	35s
Python 3.10 / dj32	38s
Python 3.10 / dj41	36s
Python 3.10 / dj42	1m 21s
Python 3.10 / dj50	38s
Python 3.11 / dj32	44s
Python 3.11 / dj41	37s
Python 3.11 / dj42	36s
Python 3.11 / dj50	38s
Python 3.12 / dj32	42s
Python 3.12 / dj41	43s
Python 3.12 / dj42	43s
Python 3.12 / dj50	46s
Python 3.10 / djmain	44s
Python 3.11 / djmain	45s
Python 3.12 / djmain	52s
Indicate completion to coveralls.io	11s
	15m 10s

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