main/postmarketos-ondev: upgrade to 0.8.2

Fix #2272 (closed), the annoying read-only FS after installation bug.

I have reproduced the bug and verified that it is fixed with both FDE and non-FDE installs with QEMU.

• https://gitlab.com/postmarketOS/postmarketos-ondev/-/compare/0.8.1...0.8.2
• https://gitlab.com/postmarketOS/postmarketos-ondev/-/tags/0.8.2