Update Marker syntax for vim

[mattjmorrison]

Apparently in vim 8.2 (apparently) the heredoc syntax requires that the markers cannot be lower case and will result in an error like this:

Error detected while processing function vim_python_test_runner#RunDesiredTests:
line 1:
E221: Marker cannot start with lower case letter
File "", line 1
<< endPython
^
SyntaxError: invalid syntax
line 2:
E1042: import/export can only be used in vim9script
line 3:
E492: Not an editor command: from vim_python_test_runner import *
line 5:
E128: Function name must start with a capital or "s:": get_proper_command(desired_command, current_directory):
line 6:
E492: Not an editor command: current_line_index = vim.current.window.cursor[0]
line 7:
E492: Not an editor command: FUNCTIONS = {
line 21:
E492: Not an editor command: }
line 22:
E121: Undefined variable: FUNCTIONS

[mattjmorrison]

That, ladies, gentlemen, and non gender specific formal acknowledgement of person hood THIS is exactly the kind of speedy open source stewardship that this world needs in more ample supply. Thank you very kindly @JarrodCTaylor