Added solution of problem 176

Author: kurpenok

src/solutions/s0176_second_highest_salary.py

@@ -0,0 +1,13 @@
+import pandas as pd
+
+
+def second_highest_salary(employee: pd.DataFrame) -> pd.DataFrame:
+    unique_salaries = employee["salary"].drop_duplicates()
+    second_highest = (
+        unique_salaries.nlargest(2).iloc[-1] if len(unique_salaries) >= 2 else None
+    )
+
+    if second_highest is None:
+        return pd.DataFrame({"SecondHighestSalary": [None]})
+
+    return pd.DataFrame({"SecondHighestSalary": [second_highest]})