import-debian-package: ensure the default branch is correctly set when importing native packages

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>

tools/import-debian-package

@@ -247,6 +247,15 @@ def import_debian_dsc(
             "debian/%(version)s", str(version)
         )
 
+        # "gbp import-dsc" has a different behavior when processing native vs
+        # non-native package. For non-native packages, the default branch is set
+        # to --debian-branch whereas for native packages the default branch is
+        # set to master which confuses next steps. Thus ensure the default
+        # branch is correctly set to --debian-branch before continuing.
+        git.checkout(f"debian/{upstream_release}")
+        if "master" in git.branch():
+            git.branch("-D", "master")
+
         # gbp puts all the new changelog entries in the commit message, generating
         # big walls of text when, for instance, importing a new package for the
         # first time.