import-debian-package: avoid oversized commit messages

`gbp import-dsc` 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.
GitLab then puts the whole log message in the `CI_COMMIT_MESSAGE` env
var, which makes the runner to fail during the executor preparation
section with the error:

    exec /usr/bin/dumb-init: argument list too long

See: https://gitlab.com/gitlab-org/gitlab/-/issues/392406



To avoid that, trim the message to only keep the first line.

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

tools/import-debian-package

@@ -195,6 +195,20 @@ def import_debian_dsc(args, dsc_file: Path, upstream: str, downstream: str, vers
                         '--no-pristine-tar',
                         str(dsc_file)]) == 0: # success
         debian_tag = DebianGitRepository.version_to_tag("debian/%(version)s", str(version))
+
+        # 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.
+        # GitLab then puts the whole log message in the CI_COMMIT_MESSAGE env var,
+        # which makes the runner to fail during the executor preparation
+        # section with the error:
+        #   exec /usr/bin/dumb-init: argument list too long
+        # See: https://gitlab.com/gitlab-org/gitlab/-/issues/392406
+        # to avoid that, trim the message to only keep the first line
+        shortmessage = git("log", "--format=%s", "-n1")
+        git("commit", "--amend", f"--message={shortmessage}")
+        git.tag('-a', '-f', '-m', f'Debian version {version}', debian_tag)
+
         epochless = Version(version)
         epochless.epoch = None
         epochless_tag = DebianGitRepository.version_to_tag("debian/%(version)s", str(epochless))