fix: build docs on fork (#1800)

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### Description

See #1799. Not sure if this is the solution you are looking for..

docs/generate_docs.py

@@ -28,7 +28,13 @@
     "test.py",
     ".pytest_cache",
 } | SCRIPTS
-TAG = subprocess.check_output(["git", "describe", "--tags"]).decode().strip()
+
+_REPO_OWNER = subprocess.check_output(["git", "remote", "-v"]).decode().strip()
+_REPO_OWNER = _REPO_OWNER.split(":")[-1].split("/")[0]
+if _REPO_OWNER == "snakemake":
+    TAG = subprocess.check_output(["git", "describe", "--tags"]).decode().strip()
+else:
+    TAG = "UNDEFINED"
 
 
 with open(os.path.join(BASE_DIR, "_templates", "tool.rst")) as f: