fix os.getenv_opt used in string interpolation, discovered through vl…

…ang/v PR#17566

src/nohup/nohup.v

@@ -2,7 +2,7 @@ import os
 import common
 
 const tool_name = 'nohup'
-const out_files = ['nohup.out', '${os.getenv_opt('HOME')!}/nohup.out']
+const out_files = ['nohup.out', '${os.getenv_opt('HOME')?}/nohup.out']
 
 fn open_nohup_out(mut f os.File, print_message bool) ! {
 	for file in out_files {