fix: Proper string for invalid SVG (#4191)

src/locales/en.json

     "imageInsertError": "Couldn't insert image. Try again later...",
     "fileTooBig": "File is too big. Maximum allowed size is {{maxSize}}.",
     "svgImageInsertError": "Couldn't insert SVG image. The SVG markup looks invalid.",
-    "invalidSVGString": "errors.invalidSVGString"
+    "invalidSVGString": "Invalid SVG."
   },
   "toolBar": {
     "selection": "Selection",