fix(ert): ERT test fails on Emacs 30+ #1024

Job	Run time
test (ubuntu-latest, 26.3, false)	53s
test (ubuntu-latest, 27.2, false)	55s
test (ubuntu-latest, 28.2, false)	59s
test (ubuntu-latest, 29.4, false)	1m 5s
test (macos-latest, 28.2, false)	1m 35s
test (macos-latest, 29.4, false)	1m 49s
test (windows-latest, 26.3, false)	4m 15s
test (windows-latest, 27.2, false)	2m 1s
test (windows-latest, 28.2, false)	1m 56s
test (windows-latest, 29.4, false)	1m 35s
test (ubuntu-latest, snapshot, true)	1m 0s
test (macos-latest, snapshot, true)	1m 33s
test (windows-latest, snapshot, true)	3m 59s
	23m 35s

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