chore(deps): update dependency pypandoc to v1.8 (#1309)

Author: renovate-bot

packages/gapic-generator/requirements.txt

@@ -4,7 +4,7 @@ googleapis-common-protos==1.56.0
 jinja2==3.1.2
 MarkupSafe==2.1.1
 protobuf==3.20.1
-pypandoc==1.7.5
+pypandoc==1.8
 PyYAML==6.0
 dataclasses==0.6  # TODO(busunkim) remove when 3.6 support is dropped
 setuptools==62.1.0