version checksum mismatch: warn rather than assert

There's a chance checksum mismatch might simply be due to inconsistent
serialization. Avoid breakage in that case.

src/pypdfium2/version.py

@@ -5,9 +5,12 @@
 
 import json
 import hashlib
+import logging
 from pathlib import Path
 import pypdfium2_raw
 
+logger = logging.getLogger(__name__)
+
 
 def _hash_data(data):
     return hashlib.md5(json.dumps(data).encode()).hexdigest()
@@ -16,7 +19,9 @@ def _load_info(fp):
     with open(fp, "r") as buf:
         data = json.load(buf)
     checksum = data.pop("_checksum_")
-    assert _hash_data(data) == checksum, f"{'/'.join(fp.parts[-2:])} checksum mismatch - file corrupt or inconsistent serialization."
+    if not _hash_data(data) == checksum:
+        data["version"] += "!invalid"
+        logger.critical(f"Caution: {'/'.join(fp.parts[-2:])} checksum mismatch - file corrupt or inconsistent serialization. Please submit a bug report if you did not touch the data.")
     return data