Improve CI schedules doc based on Vale warnings/suggestions

Unless you're a Tichtov student, please do not take this issue, or create an MR for it.

Problem to solve

The Vale linter is used to support grammar linting in GitLab documentation. As Vale was implemented after many of the GitLab documents were written, we have many documentation pages that do not meet the linting standards created by the GitLab Technical Writing team for Vale.

Further details

As an example, here's the output from a Vale test on the doc/pipelines/schedules.md file:

 schedules.md

 19:3    suggestion  Usage check: Use "once" for     gitlab.AfterOnce
                     counting ("Run a job once...")
                     and "after" for a sequence
                     ("Run this job after...").
 59:1    warning     Shorter sentences improve       gitlab.SentenceLength
                     readability (max 25 words).
 59:57   warning     Avoid using future tense:       gitlab.FutureTense
                     "will be". Use present tense
                     instead.
 66:1    warning     Shorter sentences improve       gitlab.SentenceLength
                     readability (max 25 words).
 88:15   warning     Avoid using future tense:       gitlab.FutureTense
                     "won't be". Use present tense
                     instead.
 91:33   warning     Avoid using future tense:       gitlab.FutureTense
                     "will be". Use present tense
                     instead.
 105:1   suggestion  Usage check: Use "once" for     gitlab.AfterOnce
                     counting ("Run a job once...")
                     and "after" for a sequence
                     ("Run this job after...").
 115:6   warning     Avoid using future tense:       gitlab.FutureTense
                     "will schedule". Use present
                     tense instead.
 116:9   warning     Avoid using future tense:       gitlab.FutureTense
                     "will provide". Use present
                     tense instead.
 119:70  suggestion  Usage check: Use "once" for     gitlab.AfterOnce
                     counting ("Run a job once...")
                     and "after" for a sequence
                     ("Run this job after...").
 127:57  warning     Avoid using future tense:       gitlab.FutureTense
                     "will be". Use present tense
                     instead.
 131:1   warning     Shorter sentences improve       gitlab.SentenceLength
                     readability (max 25 words).
 132:46  warning     Avoid using future tense:       gitlab.FutureTense
                     "will stop". Use present tense
                     instead.

Each of these messages point to a specific line:column in the noted file.

Proposal

Consider each error message, and see if you can rewrite the noted file with a solution. You do NOT need to address all issues in the list, this is simply the full output from Vale.

Who can address the issue

Anyone with an understanding of basic written US English. Ideally, that person should also have some domain expertise in the subject area.

Additional notes

We appreciate any help that you can provide. If you cannot resolve some of the issues, that is OK, your contributions are still appreciated. And thank you!