treewide: use Fatal in tests instead of Error

Error doesn't return the goroutine, but these cases are final and should end the test case.

Change-Id: I9d87e268b56acd7d1ff5883bb82bf3d74c309176
Reviewed-on: https://review.monogon.dev/c/monogon/+/4044
Reviewed-by: Jan Schär <jan@monogon.tech>
Tested-by: Jenkins CI
diff --git a/osbase/erofs/erofs_test.go b/osbase/erofs/erofs_test.go
index cc02047..7ab4f51 100644
--- a/osbase/erofs/erofs_test.go
+++ b/osbase/erofs/erofs_test.go
@@ -251,7 +251,7 @@
 			}
 			_ = file.Close()
 			if err := os.MkdirAll("/test", 0755); err != nil {
-				t.Error(err)
+				t.Fatal(err)
 			}
 			if err := unix.Mount("/dev/ram0", "/test", "erofs", unix.MS_NOEXEC|unix.MS_NODEV, ""); err != nil {
 				t.Fatal(err)