OBS: don't downgrade version in debian/changelog

Fix the bug that the version in debian/changelog could get lowered if a
release was made and the release git tag was not pushed yet.

Fixes: OS#6173
Change-Id: I550ed10a60c863626d870e35034028f0bd066211

scripts/obs/data/build_srcpkg.Dockerfile

@@ -18,6 +18,7 @@ RUN	apt-get update && \
 		libxml2-utils \
 		meson \
 		osc \
+		python3-packaging \
 		python3-setuptools \
 		rebar3 \
 		sed \

scripts/obs/lib/config.py

@@ -25,6 +25,7 @@ required_programs = [
 ]
 
 required_python_modules = [
+    "packaging",
     "setuptools",
 ]
 

scripts/obs/lib/debian.py

@@ -7,6 +7,13 @@ import shlex
 import lib
 import lib.git
 
+# Imports that may not be available during startup, ignore it here and rely on
+# lib.check_required_programs() checking this later on (possibly after the
+# script executed itself in docker if using --docker).
+try:
+    import packaging.version
+except ImportError:
+    pass
 
 def control_add_depend(project, pkgname, version):
     """ :param pkgname: of the meta-package to depend on (e.g. osmocom-nightly)
@@ -89,6 +96,16 @@ def changelog_add_entry_if_needed(project, version):
     """ Adjust the changelog if the version in the changelog is different from
         the given version. """
     version_changelog = get_last_version_from_changelog(project)
+
+    # Don't use a lower number (OS#6173)
+    if packaging.version.parse(version_changelog.split("-")[0]) > \
+            packaging.version.parse(version.split("-")[0]):
+        print(f"{project}: WARNING: version from changelog"
+              f" ({version_changelog}) is higher than version based on git tag"
+              f" ({version}), using version from changelog (git tag not pushed"
+              " yet?)")
+        return
+
     if version_changelog == version:
         return