Mark promoted InfixT names as IsPromoted (#17394)

We applied a similar fix for `ConT` in #15572 but forgot to apply the
fix to `InfixT` as well. This patch fixes #17394 by doing just that.
21 jobs for master in 2 minutes and 16 seconds (queued for 1 second)
Name Stage Failure
lint-submods-branch Lint
Fetching origin
Entering 'utils/haddock'
Fetching origin
Entering 'utils/hsc2hs'
Fetching origin
$ submodchecker .git $(git rev-list $CI_COMMIT_BEFORE_SHA..$CI_COMMIT_SHA)
Submodule update(s) detected in 6beea836094383eea96b15e526f31b5426aea630:
*FAIL* commit message does not contain magic 'submodule' word
ERROR: Job failed: exit code 1