Stop raising exceptions on unexpected ]]] characters

[kurtmckee]

This addresses errors that occur on valid files, like GitHub workflows that contain both cog usage and embedded Python with accurate type annotations. For example:

on:
  push:
jobs:
  demo:
    runs-on: ubuntu-latest
    steps:
      - run: |
          # [[[cog cog.outl("echo 'hello'") ]]]
          echo 'hello'
          # [[[end]]]
      - shell: python
        run: |
          def demo() -> tuple[tuple[tuple[str]]]:
              #                              ^^^
              # This caused a failure        |||
              #
              return ((("hello world",),),)
          print(demo()[0][0][0])

Fixes #52

[nedbat]

This makes sense. When cog started, I didn't imagine ]]] would occur in the wild!

[kurtmckee]

Thanks for reviewing and merging this, @nedbat!