missing comma in MIME_TYPES makes Graphviz render blocks that it should not

[ebouaziz@…]

on line 193, MIME_TYPES = ('application/graphviz') makes MIME_TYPES a string instead of a tuple.

This makes Graphviz's get_quality_ratio() return 2 and be selected to render a block that has for example the #!c shebang. This will fail and render dot's error message in a red rectangle.

fix: MIME_TYPES = ('application/graphviz',)

[Ryan J Ollos]

In 17422:

1.0.0.8dev: Fix incorrect application of graphviz renderer

Change is merged to 1.0.0.9dev (1.2 branch) and
1.3.0.1dev (trunk).

Fix by ebouaziz@….

Refs #13579.