Fix runner compatibility matrix glitch

[Abacn]

Please add a meaningful description for your change here

Two glitches:

1. the left column and the remaining are not aligned:

2. scroll the table horizontally, the caption row and data row doesn't move together:

Both are fixed for now.

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[github-actions]

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R: @damccorm for label website.

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[Abacn]

After fix: https://apache-beam-website-pull-requests.storage.googleapis.com/39682/documentation/runners/capability-matrix/index.html

[damccorm]

Thanks!