Make sure InvalidVarException.fail is reset #344

Job	Run time
deploy	0s
test (linting,docs, 3.11, false)	49s
test (py311-dj42-postgres-xdist-coverage, 3.11, false)	2m 58s
test (py310-dj41-postgres-xdist-coverage, 3.10, false)	3m 1s
test (py310-dj32-postgres-xdist-coverage, 3.10, false)	3m 2s
test (py311-dj41-mysql_innodb-coverage, 3.11, false)	2m 19s
test (py310-dj42-mysql_innodb-coverage, 3.10, false)	4m 12s
test (py39-dj32-mysql_innodb-xdist-coverage, 3.9, false)	3m 2s
test (py38-dj41-sqlite-xdist-coverage, 3.8, false)	1m 55s
test (py37-dj32-sqlite-xdist-coverage, 3.7, false)	2m 21s
test (py310-djmain-sqlite-coverage, 3.10, true)	2m 4s
test (py37-dj32-mysql_myisam-coverage, 3.7, false)	2m 24s
test (py37-dj32-sqlite-pytestmin-coverage, 3.7, false)	1m 54s
test (pypy3-dj32-postgres, pypy3.9, false)	4m 15s
	34m 16s

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