Fix leap year condition in monthly means example (pydata#3464)

* Typo correction in docs (pydata#3387)

* Update terminology.rst (pydata#3455)

Fixed broken link

* Error in leap year?

I've tried this script; however, it adds +1 to all months of the leap years. It sounds like an error, or I am wrong? So I wrote the condition "and month == 2" line 86 so that only the month of February gets +1.

* Fix leap year (pydata#3464)

* Update doc/whats-new.rst

Co-Authored-By: Deepak Cherian <dcherian@users.noreply.github.com>

doc/examples/monthly-means.ipynb

@@ -107,7 +107,7 @@
     "    \n",
     "    for i, (month, year) in enumerate(zip(time.month, time.year)):\n",
     "        month_length[i] = cal_days[month]\n",
-    "        if leap_year(year, calendar=calendar):\n",
+    "        if leap_year(year, calendar=calendar) and month == 2:\n",
     "            month_length[i] += 1\n",
     "    return month_length"
    ]