Fix error location for class patterns

[sobolevn]

Now it uses the same pattern for .fail as similar places:

• mypy/mypy/checkpattern.py

  Line 459 in 2d8ad8e

  self.msg.fail(message_registry.CLASS_PATTERN_GENERIC_TYPE_ALIAS, o)

• mypy/mypy/checkpattern.py

  Line 493 in 2d8ad8e

  self.msg.fail(message_registry.CLASS_PATTERN_TOO_MANY_POSITIONAL_ARGS, o)

• etc

Test proves that this problem is now fixed.
Closes #15496

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅