fixup! MB 1: Mullvad Browser branding

Bug 42490: Write the browser logo SVG also outside of omni.ja.

For Mullvad Browser, we have to add this also to the various moz.build
that are inside each branding directory, because we do not call
FirefoxBranding for them.

browser/branding/mb-alpha/moz.build

@@ -23,6 +23,7 @@ if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'windows':
     ]
 elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gtk':
     FINAL_TARGET_FILES.chrome.icons.default += [
+        'content/about-logo.svg',
         'default128.png',
         'default16.png',
         'default256.png',

browser/branding/mb-nightly/moz.build

@@ -23,6 +23,7 @@ if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'windows':
     ]
 elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gtk':
     FINAL_TARGET_FILES.chrome.icons.default += [
+        'content/about-logo.svg',
         'default128.png',
         'default16.png',
         'default256.png',

browser/branding/mb-release/moz.build

@@ -23,6 +23,7 @@ if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'windows':
     ]
 elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gtk':
     FINAL_TARGET_FILES.chrome.icons.default += [
+        'content/about-logo.svg',
         'default128.png',
         'default16.png',
         'default256.png',