MacOS 10.15 boxes cannot upgrade all packages with brew

ref https://github.com/adoptium/infrastructure/pull/3045

MacOS 10.15 is out of support https://endoflife.date/macos. As a temp fix for the sake of preventing playbook crashes I have skipped the `upgrade_all` task on our macos 10.15 and under boxes but we need a better solution

```
TASK [Common : Upgrade installed packages] *************************************
fatal: [test-macstadium-macos1015-x64-1]: FAILED! => {"changed": false, "msg": "Warning: You are using macOS 10.15.\n
We (and Apple) do not provide support for this old version.\n
It is expected behaviour that some formulae will fail to build in this old version.\n
It is expected behaviour that Homebrew will be buggy and slow.\n
Do not create any issues about this on Homebrew's GitHub repositories.\n
Do not create any issues even if you think this message is unrelated.\n
Any opened issues will be immediately closed without response.\n
Do not ask for help from Homebrew or its maintainers on social media.\n
You may ask for help in Homebrew's discussions but are unlikely to receive a response.\n
Try to figure out the problem yourself and submit a fix as a pull request.\n
We will review it but may or may not accept it.\n\n
Error: Your Xcode (10.3) is too outdated.\nPlease update to Xcode 12.4 (or delete it).\n
Xcode can be updated from the App Store."}

```
@sxa Are we able to have these boxes upgraded?

Our 10.14 and 10.15 boxes make up 7/9 of our x64 mac machines, the other 2 being 12.01

Review pull request 3045 and the `upgrade_all` task responsible for upgrading packages on macOS 10.14 and 10.15 boxes. Determine how the maintenance playbook should handle these unsupported systems, then verify the playbook no longer crashes while preserving package upgrades where possible.

Written by the indexing model from the issue text.