RELEASE.md: tweak push step [no ci]

Instead of pushing to master and the tag in the same
command, let's separate it because I just got a case
in which master received the commit before the tag
(even if the tag appears first in the push command)
and then a pre-release was created in nuget because of
that. This should not happen if the tag is already there
when the CI for master branch starts, thanks to this fix
from some time ago:
fa788db

Author: knocte

RELEASE.md

@@ -6,7 +6,7 @@ Revision (Z) part of the version by 2, e.g.: `0.23.2 -> 0.24.0` or `0.23.2 -> 1.
 (ideally one line per PR or commit).
 3. Commit (e.g. with a title such as "Bump version to `X.Y.Z` adding release notes"), but don't push yet!
 4. Tag the head of master with the version number in the format `vX.Y.Z` - e.g.: `git tag v0.20.4`.
-5. Push to remote: `git push origin vX.Y.Z master` - this will start CI processes that will:
+5. Push to remote: `git push origin vX.Y.Z && git push origin master` - this will start CI processes that will:
 * Build the package
 * Create a github release
 * Pushes the package to NuGet