Fix: make update-toc error in mac os

[dongjiang1989]

Fix make update-toc error in mac os:

     Checking table of contents are up to date...
     2026/04/08 20:10:08 docs/keps/359-refactor-python-sdk/README.md: missing opening TOC tag
     2026/04/08 20:10:08 docs/keps/174-metadata-propagation/README.md: missing opening TOC tag
     Table of content not up to date. Did you run 'make update-toc' ?                                                   
     If this failed silently and you are on mac, try 'brew install grep'
     Cleaning up...   

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[aditya-shantanu]

/lgtm
/approve

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This pull-request has been approved by: aditya-shantanu, dongjiang1989
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[aditya-shantanu]

/assign @barney-s