docs: Add missing RELEASE_BRANCH code block for 1-35

[varma-maryala]

Problem

The 1-35 section in index.md is missing the code block that the release-docs automation script expects.

Impact

Running RELEASE_BRANCH=1-35 make release-docs fails with:

updating index file because did not find line "RELEASE_BRANCH=1-35"

Solution

Add the missing code block that matches the format used by all other versions (1-29 through 1-34).

Testing

After this merges, RELEASE_BRANCH=1-35 make release-docs will work correctly.

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[varma-maryala]

Closing - incorrect fix. The code block should be in the general section at top, not in the version-specific section.