This pull request fixes an issue with the regex for the Comment.Single token type in the TransactSqlLexer class.

In the current version of pygments (2.18.0), the existing regex causes single-line comments to be lexed incorrectly whenever they are immediately followed by a non-comment token on the next line. For example, consider the following code:

from pygments.lexers.sql import TransactSqlLexer
for token_type, token_contents in list(
    TransactSqlLexer().get_tokens(
        """
        -- this is a single line comment
        select
        """
    )
):
    print(token_type, repr(token_contents))

When run, this results in the following stream of tokens: (Note that the comment is lexed as various other tokens)

Token.Text.Whitespace '        '
Token.Operator '-'
Token.Operator '-'
Token.Text.Whitespace ' '
Token.Name 'this'
Token.Text.Whitespace ' '
Token.Keyword 'is'
Token.Text.Whitespace ' '
Token.Name 'a'
Token.Text.Whitespace ' '
Token.Name 'single'
Token.Text.Whitespace ' '
Token.Name 'line'
Token.Text.Whitespace ' '
Token.Name 'comment'
Token.Text.Whitespace '\n        '
Token.Keyword 'select'
Token.Text.Whitespace '\n        \n'

Lexing with the modified regex for the token Comment.Single in this commit results in the following stream of tokens: (Note that the comment is now lexed correctly.)

Token.Text.Whitespace '        '
Token.Comment.Single '-- this is a single line comment\n'
Token.Text.Whitespace '        '
Token.Keyword 'select'
Token.Text.Whitespace '\n        \n'