docs(bigquery): fix table rendering in markdown docs

[shuoweil]

This monkeypatch is an isolated workaround in docs/conf.py while a permanent upstream fix is not scheduled in gcp-sphinx-docfx-yaml.

Fixes table formatting in the generated Markdown reference documentation for google-cloud-bigquery.
When building Markdown documentation via sphinx-markdown-builder, table cell paragraphs unconditionally emit trailing newlines. This breaks single-line GitHub Flavored Markdown (GFM) table rows, causing cell padding to be interpreted as 4-space indented code blocks on reference doc pages.

This change adds a targeted patch in docs/conf.py that suppresses newlines when exiting paragraphs inside table cells, restoring valid GFM table syntax.

before: screen/3oup25c57irb8
after: screen/4GqUXF7gs4p6GZV (render locally with nox -s doxfx)

Fixes #<522853190> 🦕

[gemini-code-assist]

Code Review

This pull request introduces a workaround in docs/conf.py to suppress trailing newlines in table cells generated by sphinx-markdown-builder, preserving valid GFM tables. It also adds a unit test to verify that docs/conf.py executes successfully. The reviewer recommended gracefully skipping this new unit test if docs/conf.py is not found, which can happen when tests are run against an installed package where the docs/ directory is absent.