[jnigen] Fix flaky tests #20

Job	Run time
build_jni_example_linux	1m 24s
analyze_jni	55s
analyze_jnigen (stable)	34s
build_jni_example_android	3m 7s
build_jni_example_windows	3m 55s
run_pdfbox_example_linux	2m 40s
test_jnigen_macos_minimal	8m 13s
test_jnigen (ubuntu-latest, stable)	8m 43s
test_jnigen_windows_minimal	10m 57s
test_jnigen (ubuntu-latest, beta)	8m 40s
test_jni	2m 10s
test_jni_macos_minimal	2m 28s
test_jni_windows_minimal	7m 38s
coveralls_finish	0s
	1h 1m 24s

Provide feedback