fix(scripts/yaml_check.py): more consistent error handling (#20614)

Invalid fields in the 100.yaml and 1000.yaml files are slipping through CI at the moment, see e.g. [this log](https://github.com/leanprover-community/mathlib4/actions/runs/12690334474/job/35370960547#step:19:8).

After this commit, all errors detected by `yaml_check.py` print a message and increment the `errors` variable, only failing at the end of the script (so that all entries can get checked).

scripts/yaml_check.py

@@ -110,6 +110,7 @@ class ThousandPlusTheorem:
     _thm = HundredTheorem(index, **entry)
   except TypeError as e:
     print(f"error: entry for theorem {index} is invalid: {e}")
+    errors += 1
   # Also verify that the |decl| and |decls| fields are not *both* provided.
   if _thm.decl and _thm.decls:
       print(f"warning: entry for theorem {index} has both a decl and a decls field; "
@@ -121,7 +122,8 @@ class ThousandPlusTheorem:
     hundred_decls.append((f'{index} {title}', entry['decl']))
   elif 'decls' in entry:
     if not isinstance(entry['decls'], list):
-      raise ValueError(f"For key {index} ({title}): did you mean `decl` instead of `decls`?")
+      print(f"For key {index} ({title}): did you mean `decl` instead of `decls`?")
+      errors += 1
     hundred_decls = hundred_decls + [(f'{index} {title}', d) for d in entry['decls']]
 
 thousand_decls: List[Tuple[str, str]] = []
@@ -131,6 +133,7 @@ class ThousandPlusTheorem:
     _thm = ThousandPlusTheorem(index, **entry)
   except TypeError as e:
     print(f"error: entry for theorem {index} is invalid: {e}")
+    errors += 1
   # Also verify that the |decl| and |decls| fields are not *both* provided.
   if _thm.decl and _thm.decls:
       print(f"warning: entry for theorem {index} has both a decl and a decls field; "
@@ -142,7 +145,8 @@ class ThousandPlusTheorem:
     thousand_decls.append((f'{index} {title}', entry['decl']))
   elif 'decls' in entry:
     if not isinstance(entry['decls'], list):
-      raise ValueError(f"For key {index} ({title}): did you mean `decl` instead of `decls`?")
+      print(f"For key {index} ({title}): did you mean `decl` instead of `decls`?")
+      errors += 1
     thousand_decls = thousand_decls + [(f'{index} {title}', d) for d in entry['decls']]
 
 overview_decls = tiered_extract(overview)
@@ -163,4 +167,5 @@ class ThousandPlusTheorem:
   json.dump(undergrad_decls, f)
 
 if errors:
-  sys.exit(errors)
+  # Return an error code of at most 125 so this return value can be used further in shell scripts.
+  sys.exit(min(errors, 125))