Re-enable conditional building of protocol spec PDFs.

For the publish step, this requires setting `base_ref` before merging to
`main`.

Signed-off-by: Daira-Emma Hopwood <daira@jacaranda.org>

ZIP 321: Fix a reference error.

Signed-off-by: Daira-Emma Hopwood <daira@jacaranda.org>

ZIP 214: set the `FS_FPF_ZCG_H3` Mainnet address (same as the one for

Revision 1).

Signed-off-by: Daira-Emma Hopwood <daira@jacaranda.org>

Protocol spec: set correct release date.

Signed-off-by: Daira-Emma Hopwood <daira@jacaranda.org>

Set Change History date for v2024.5.1.

Signed-off-by: Daira-Emma Hopwood <daira@jacaranda.org>

Regenerate PDFs.

Set Change History date for 2024.5.0.

Signed-off-by: Daira-Emma Hopwood <daira@jacaranda.org>

Regenerate PDFs.

Signed-off-by: Daira-Emma Hopwood <daira@jacaranda.org>

Rename `release` Makefile target to `tag-release`. Make it not requir…

…e being on main,

but check that the current branch is a descendant of the `origin` remote's `main`, i.e.
pushing to `origin main` would be a fast-forward.

Signed-off-by: Daira Emma Hopwood <daira@jacaranda.org>

Regenerate PDFs.