[3.4] Fix grammar in uptime command (#5596) (#5738)

(cherry picked from commit 58d8cb4)

Co-authored-by: TrustyJAID <TrustyJAID@gmail.com>

Co-authored-by: TrustyJAID <TrustyJAID@gmail.com>

redbot/core/core_commands.py

@@ -535,7 +535,7 @@ async def uptime(self, ctx: commands.Context):
         uptime = self.bot.uptime.replace(tzinfo=datetime.timezone.utc)
         uptime_str = humanize_timedelta(timedelta=delta) or _("Less than one second.")
         await ctx.send(
-            _("Been up for: **{time_quantity}** (since {timestamp})").format(
+            _("I have been up for: **{time_quantity}** (since {timestamp})").format(
                 time_quantity=uptime_str, timestamp=f"<t:{int(uptime.timestamp())}:f>"
             )
         )