pyyaml can't parse the character = in some places

[thatch]

The special value tag appears to be unhandled in several locations. For example,

>>> from yaml import load, Loader
>>> load("=:", Loader=Loader)
{'=': None}
>>> load("=", Loader=Loader)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/timhatch/code/codemod-yaml/.venv/lib/python3.12/site-packages/yaml/__init__.py", line 81, in load
    return loader.get_single_data()
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/timhatch/code/codemod-yaml/.venv/lib/python3.12/site-packages/yaml/constructor.py", line 51, in get_single_data
    return self.construct_document(node)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/timhatch/code/codemod-yaml/.venv/lib/python3.12/site-packages/yaml/constructor.py", line 55, in construct_document
    data = self.construct_object(node)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/timhatch/code/codemod-yaml/.venv/lib/python3.12/site-packages/yaml/constructor.py", line 100, in construct_object
    data = constructor(self, node)
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/timhatch/code/codemod-yaml/.venv/lib/python3.12/site-packages/yaml/constructor.py", line 427, in construct_undefined
    raise ConstructorError(None, None,
yaml.constructor.ConstructorError: could not determine a constructor for the tag 'tag:yaml.org,2002:value'
  in "<unicode string>", line 1, column 1:
    =
    ^

but it's not just a bug at the root of document, see

>>> load("=: =", Loader=Loader)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/timhatch/code/codemod-yaml/.venv/lib/python3.12/site-packages/yaml/__init__.py", line 81, in load
    return loader.get_single_data()
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/timhatch/code/codemod-yaml/.venv/lib/python3.12/site-packages/yaml/constructor.py", line 51, in get_single_data
    return self.construct_document(node)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/timhatch/code/codemod-yaml/.venv/lib/python3.12/site-packages/yaml/constructor.py", line 60, in construct_document
    for dummy in generator:
                 ^^^^^^^^^
  File "/Users/timhatch/code/codemod-yaml/.venv/lib/python3.12/site-packages/yaml/constructor.py", line 413, in construct_yaml_map
    value = self.construct_mapping(node)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/timhatch/code/codemod-yaml/.venv/lib/python3.12/site-packages/yaml/constructor.py", line 218, in construct_mapping
    return super().construct_mapping(node, deep=deep)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/timhatch/code/codemod-yaml/.venv/lib/python3.12/site-packages/yaml/constructor.py", line 143, in construct_mapping
    value = self.construct_object(value_node, deep=deep)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/timhatch/code/codemod-yaml/.venv/lib/python3.12/site-packages/yaml/constructor.py", line 100, in construct_object
    data = constructor(self, node)
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/timhatch/code/codemod-yaml/.venv/lib/python3.12/site-packages/yaml/constructor.py", line 427, in construct_undefined
    raise ConstructorError(None, None,
yaml.constructor.ConstructorError: could not determine a constructor for the tag 'tag:yaml.org,2002:value'
  in "<unicode string>", line 1, column 4:
    =: =
       ^