Is there a tool to update my PPA sources.list entries after upgrading?

There is a tool called Y-PPA-Manager that lets you do exactly that.

To try Y-PPA-Manager, you need to run the following commands in a terminal:

sudo add-apt-repository ppa:webupd8team/y-ppa-manager
sudo apt-get update
sudo apt-get install y-ppa-manager

After installing, run the software and click on 'Advanced' button.

After clicking on that button, you would come up with a window similar to the one below. Click on 'Re-enable working PPAs after Ubuntu upgrade'.

You would then be prompted for your password. Enter your password and click OK. After that, you would get a dialog box like this:

Click OK and wait till all the working PPAs are re-enabled. When the entire process is successfully completed, you would be notified.

There is an intriguing simple command as you can now keep PPAs and Third Party Repositories enabled when upgrading to a newer Ubuntu version:

RELEASE_UPGRADER_ALLOW_THIRD_PARTY=1 do-release-upgrade -d

The RELEASE_UPGRADER_ALLOW_THIRD_PARTY environment variable can be used with both the command line and the GUI upgrade tools. So when you want to upgrade your Ubuntu system and keep PPA and third party repositories enabled, run the upgrade from a terminal, like mentioned above for the command version. I guess BEFORE the actual system upgrading. For the GUI version:

RELEASE_UPGRADER_ALLOW_THIRD_PARTY=1 update-manager -d

(-d is used to allow upgrading to development releases - for example to upgrade from Ubuntu 18.10 to 19.04 right now, while Ubuntu 19.04 Disco Dingo is still in development)

It's worth noting that you may still see a warning about third party sources being disabled on upgrade, but those that support the Ubuntu version to which you're upgrading will not be disabled.

A regular Ubuntu release upgrade (to a newer Ubuntu version) disables any PPA or third party repository that may be enabled. Some recent changes to ubuntu-release-upgrader allow keeping PPA and third party repositories enabled when upgrading to a newer Ubuntu release, while also providing better support for cases in which the users have their own mirror of the archive. This is done by using an environment variable, RELEASE_UPGRADER_ALLOW_THIRD_PARTY.
Source: Linux Uprising Blog and Brian’s Blog

I only found this solution after the upgrade and ran the command anyway, it added a new entry for each PPA with the new Ubuntu version's name in it. I just had to delete the old ones then.