release.sh: stop doing "-dev" releases on stable branches

Note: here I refer to the numbers in a version as MAJOR.MINOR.MICRO.

Having stable and development releases do make sense for the MINOR
version, because we maintain separate branches for them and they
evolve separately. We have 1.47.z where we put all the changes so
anyone can pick the latest development release and test it. At the
same time, we have 1.46.z with the latest stable released version.

However, it does not make sense to have 1.46.2 and 1.46.3-dev because
the latter is not a development version. It is identical to 1.46.2,
only the version number has been bumped, there are no changes to test.
When we add commits, we will be actually testing 1.46.3-dev + some
commits, which is exactly the same as testing 1.46.2 + some commits.

So, basically, someone can use the releases of a development BRANCH,
like 1.47.4, to test the development version of NM. But using a
development MICRO version is exactly the same as using a
non-development one.

From now on, we will just increment the MICRO version each time we do a
release on a stable branch and won't create the '-dev' tag. Update
release.sh to do it this way.

NEWS

@@ -27,6 +27,11 @@ USE AT YOUR OWN RISK.  NOT RECOMMENDED FOR PRODUCTION USE!
   when IPv6 device address was not explicitly passed on by ModemManager
 * Fix a performance issue that was leading to 100% CPU usage by NetworkManager
   if external programs were doing a big amount of routes updates.
+* Patch-level development releases (i.e. 1.48.1-dev) won't be used anymore.
+  From now on, all the patch releases whithin a stable branch will be normal
+  releases, like 1.48.0, 1.48.1, 1.48.2, 1.48.3 and so on.
+  Odd numbers in the minor version number still indicates if it's a development
+  branch like 1.49 or a stable one like 1.48.
 
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 NetworkManager-1.46