Fix observeEvent stack trace stripping #2667

Job	Run time
R-CMD-check / setup	6s
routine / routine	4m 18s
website / pkgdown	3m 1s
R-CMD-check / macOS-latest (4.4.2)	2m 55s
R-CMD-check / windows-latest (4.4.2)	4m 59s
R-CMD-check / ubuntu-latest (devel)	3m 29s
R-CMD-check / ubuntu-latest (4.4.2)	3m 42s
R-CMD-check / ubuntu-latest (4.3.3)	3m 13s
R-CMD-check / ubuntu-latest (4.2.3)	3m 50s
R-CMD-check / ubuntu-latest (4.1.3)	3m 40s
R-CMD-check / ubuntu-latest (4.0.5)	3m 52s
	37m 5s

Provide feedback