ci: make sure -dev version suffix is not forgotten after release

Workflow checks that PRs are made only when current version ends with -dev
If this fails, a commit bumping the version to -dev should be pushed to main branch.

scripts/check-dev-version.py

@@ -0,0 +1,23 @@
+#!/usr/bin/env python3
+#
+# Script to check that current version ends with -dev.
+# Meant to be run in CI to check that PRs are made against the -dev version.
+# If the version is not -dev, it was forgotten to be updated
+# after making a release.
+
+from pathlib import Path
+import tomllib
+import sys
+
+
+def main():
+    with Path("Cargo.toml").open("rb") as fp:
+        cargo_toml = tomllib.load(fp)
+    version = cargo_toml["package"]["version"]
+    if not version.endswith("-dev"):
+        print(f"Current version {version} does not end with -dev", file=sys.stderr)
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()