Fix three doc-reference lint hits blocking every PR

[sbryngelson]

Master's Lint Toolchain has been red since #1855 (5953684), and because PR checks run against the merge with base, it fails every open PR rather than just master. #1847, #1843 and #1839 are all red on it right now.

docs/documentation/contributing.md:220 single-backtick span `$:GPU_UPDATE(device='[name]')` contains a
  single quote, which Doxygen treats as ending the span
docs/documentation/gpuParallelization.md:877 single-backtick span `GPU_ROUTINE(parallelism='[seq]')`
  contains a single quote, which Doxygen treats as ending the span
docs/documentation/testing.md:16 links to #selection-and-execution-pitfalls but no
  {#selection-and-execution-pitfalls} anchor exists

Three lines: double backticks around the two spans that contain a quote, and the anchor added to the ### Selection and Execution Pitfalls header the link already points at.

python3 toolchain/mfc/lint_docs.py and ./mfc.sh precheck both pass on this branch.

Split out of #1859 so it can go in on its own - that PR carries an unrelated m_viscous.fpp fix and will sit in review, and this is blocking everyone's CI meanwhile.

[sbryngelson]

Superseded by #1857, which covers these three plus the rest of the doc-lint cleanup.

[Copilot]

Warning

Copilot couldn't run its full agentic review because it didn't start before the timeout. Make sure your repository has a runner available, or add a copilot-code-review.yml file specifying one with the runs-on attribute. See the docs for more details.

Pull request overview

This PR fixes three documentation-reference lint failures that were causing Doxygen/doc lint checks to fail for every PR.

Changes:

• Add the missing Doxygen anchor {#selection-and-execution-pitfalls} to match an existing link target.
• Wrap two inline-code spans containing single quotes in double backticks to prevent Doxygen from prematurely terminating the code span.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
docs/documentation/testing.md	Adds the missing header anchor so existing intra-doc links resolve.
docs/documentation/gpuParallelization.md	Uses double-backtick inline code for a macro example containing single quotes.
docs/documentation/contributing.md	Uses double-backtick inline code for a $:GPU_UPDATE(...) example containing single quotes.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.