bash: fix bashrcExtra interactive shell test

To determine if bash is running interactively test whether "$-"
contains "i".

See: https://www.gnu.org/software/bash/manual/html_node/Is-this-Shell-Interactive_003f.html

modules/programs/bash.nix

@@ -155,7 +155,7 @@ in
     in mkIf cfg.enable {
       programs.bash.bashrcExtra = ''
         # Commands that should be applied only for interactive shells.
-        if [[ -n $PS1 ]]; then
+        if [[ $- == *i* ]]; then
           ${historyControlStr}
 
           ${shoptsStr}