i18n: don't translate empty string

see #7158

```
$ ./contrib/pull_locale
Found 260 files to translate
Generate template
electrum/gui/qt/installwizard.py:265: warning: Empty msgid.  It is reserved by GNU gettext:
                                               gettext("") returns the header entry with
                                               meta information, not the empty string.
electrum/gui/qt/channels_list.py:49: warning: Empty msgid.  It is reserved by GNU gettext:
                                              gettext("") returns the header entry with
                                              meta information, not the empty string.
```

electrum/gui/qt/channels_list.py

@@ -46,7 +46,7 @@ class ChannelsList(MyTreeView):
     headers = {
         Columns.SHORT_CHANID: _('Short Channel ID'),
         Columns.NODE_ALIAS: _('Node alias'),
-        Columns.FEATURES: _(''),
+        Columns.FEATURES: "",
         Columns.CAPACITY: _('Capacity'),
         Columns.LOCAL_BALANCE: _('Can send'),
         Columns.REMOTE_BALANCE: _('Can receive'),

electrum/gui/qt/installwizard.py

@@ -262,7 +262,7 @@ class InstallWizard(QDialog, MessageBoxMixin, BaseWizard):
                     self.logger.exception('')
                     msg = _('Cannot read file') + f'\n{repr(e)}'
             else:
-                msg = _('')
+                msg = ""
             self.next_button.setEnabled(temp_storage is not None)
             user_needs_to_enter_password = False
             if temp_storage:

electrum/i18n.py

@@ -33,7 +33,9 @@ language = gettext.translation('electrum', LOCALE_DIR, fallback=True)
 # note: f-strings cannot be translated! see https://stackoverflow.com/q/49797658
 #       So this does not work:   _(f"My name: {name}")
 #       instead use .format:     _("My name: {}").format(name)
-def _(x):
+def _(x: str) -> str:
+    if x == "":
+        return ""  # empty string must not be translated. see #7158
     global language
     return language.gettext(x)