Add GHA JP5.12 & JP6 builds

[Nir-Az]

@dmipx when trying to prepare JP5.1.2 workspace I get an error:

2024-04-01T19:50:39.5050054Z Downloading default 3rdparty/dtc source...
2024-04-01T19:50:39.5058990Z Cloning into 'sources_5.1.2/3rdparty/dtc'...
2024-04-01T19:50:39.9323745Z The default 3rdparty/dtc source is downloaded in: sources_5.1.2/3rdparty/dtc
2024-04-01T19:50:39.9336204Z Couldn't find tag jetson_35.4.1
2024-04-01T19:50:39.9336967Z sources_5.1.2/3rdparty/dtc source sync to tag jetson_35.4.1 failed!

Any idea why?

[dmipx]

LGTM