bump-ver-manifest now takes an optional parameter `--mcs` to operate
on `mcs-devel.xml` instead of `devel.xml`.

Signed-off-by: Gerwin Klein <[email protected]>

Python 3.12 complains about `\<` not being a legal escape sequence. Use
raw string instead.

Signed-off-by: Gerwin Klein <[email protected]>

Add deployment of the mcs-devel.xml manifest to mcs.xml.

The pattern is to use the branch name in `github.ref` as a guard in the
initial code freeze action, and then make any subsequent actions depend
on either `code` or `mcs-code`, respectively.

All of this lives on the master branch (but does trigger on pushes to
`rt`), so that it can in the future also trigger on manifest updates
from `repository_dispatch` events.

Currently the latter does not happen yet, because `github.ref` will be
`refs/head/master` for `repository_dispatch` events, so only the main
deployment job runs for those.

Signed-off-by: Gerwin Klein <[email protected]>

The push trigger on the PR actual was used previously for the `rt`
branch. Branch testing is now on the main deployment action.

Signed-off-by: Gerwin Klein <[email protected]>