src: Consistently spell whitespace without whitespace

Whitespace is spelled without a space between white and space, so
make sure to consistently spell it that way across the codebase.

Closes #6023
Reviewed-by: Daniel Stenberg <daniel@haxx.se>
Reviewed-by: Emil Engler <me@emilengler.com>

src/tool_parsecfg.c

@@ -227,7 +227,7 @@ int parseconfig(const char *filename, struct GlobalConfig *global)
             break;
           default:
             warnf(operation->global, "%s:%d: warning: '%s' uses unquoted "
-                  "white space in the line that may cause side-effects!\n",
+                  "whitespace in the line that may cause side-effects!\n",
                   filename, lineno, option);
           }
         }