playbook_guide/playbooks_variables.rst: improve style. Assisted-by: AI

[Andersson007]

playbook_guide/playbooks_variables.rst: improve style. Assisted-by: AI

make it satisfy only the following exhaustive list of requirements:
- Produce an RST snippet
- Consider reorganizing RST notes as simple text
- Do not modify the original indentation including code snippets
- You can add more sections, but do not change any existing headings, RST anchors/references
- Generally, use a sentence to introduce a list that is not a procedure
- Fix ambiguous pronouns. Avoid sentences in which a pronoun can refer to more than one noun or in which a pronoun refers to an unstated noun
- When you break a long procedure or tutorial into smaller chunks, include a summary at the start of the procedure or tutorial
- Spell out unknown abbreviations at the first instance
- Use US spelling
- Use present tense
- Use active voice as much as possible
- Use second person (you)
- Avoid first person (I, we, us)
- Place the word "only" immediately before the word or phrase that it modifies
- Use sentence-style capitalization for titles and headings
- Do not use uppercase letters for emphasis
- Do not start a sentence with a lowercase term; rewrite the sentence
- Capitalize the first word of each item in a vertical or definition list
- Use sentence-style capitalization for these table elements: cell contents, column headings, row labels, table captions
- Use "while" only to refer to a period of time. Do not use "while" as a synonym for although or though
- Use "once" to mean one time. Do not use "once" as a conjunction to mean "after" or "when"

[Andersson007]

ready for review

[patchback]

Backport to stable-2.17: 💚 backport PR created

✅ Backport PR branch: patchback/backports/stable-2.17/7a35c9b7c54c15f091ad58a94148335274a4de9b/pr-2916

Backported as #2925

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to stable-2.18: 💚 backport PR created

✅ Backport PR branch: patchback/backports/stable-2.18/7a35c9b7c54c15f091ad58a94148335274a4de9b/pr-2916

Backported as #2926

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to stable-2.19: 💚 backport PR created

✅ Backport PR branch: patchback/backports/stable-2.19/7a35c9b7c54c15f091ad58a94148335274a4de9b/pr-2916

Backported as #2927

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.