[5.8.1, 5.8.2, 5.8.3, 5.8.4, 5.8.5, 5.8.6, 5.8.7, 5.8.8, 5.8.9, 5.8.10, 5.8.11, 5.8.12, 5.8.13, 5.8.14, 5.8.15, 5.8.16, 5.8.17, 5.8.18, 5.9.1, 5.9.2, 5.9.3, 5.9.4, 5.9.5, 5.9.6, 5.9.7, 5.9.8, 5.9.9, 5.9.10, 5.9.11, 5.9.12, 5.9.13, 5.9.14, 5.9.15, 5.9.16, 5.10.1, 5.10.2, 5.10.3, 5.10.4, 5.10.5, 5.10.6]

$ cat latest-versions.py 
import requests
from bs4 import BeautifulSoup

latest, prev = "", ""
result = []
r = requests.get("https://kernel.ubuntu.com/~kernel-ppa/mainline/") 
if r.status_code != 200:
    print(f"{r.status_code=}")
    exit(1)

soup = BeautifulSoup(r.text, "lxml")
table = soup.find('table')
for tr in table.find_all('tr'):
    for ind, td in enumerate(tr.find_all('td')):
        if ind == 1: 
            abc = td.text[1:-1].split(".")
            if len(abc) == 3:
                a, b, c = abc
                if latest == f"{a}{b}":
                    prev = f"{a}.{b}.{c}"
                else:
                    latest = f"{a}{b}"
                    if prev:
                        result = [prev] + result
result = [prev] + result
print(result)