[16.0][FIX] hr_holidays_summary_email: change message if empty summary

[MiquelRForgeFlow]

Avoid having a mail with:

[OCA-git-bot]

Hi @JordiMForgeFlow,
some modules you are maintaining are being modified, check this out!

[JoanSForgeFlow]

Hi @MiquelRForgeFlow,

Not receiving any emails can also be a bit confusing. How about we mention in the email that no one is on vacation this week?

Thanks!

[MiquelRForgeFlow]

Not receiving any emails can also be a bit confusing.

In my opinion, the empty summary is spam haha

How about we mention in the email that no one is on vacation this week?

Done.

[GuillemCForgeFlow]

amazing changes 👍🏿

[cubells]

LGTM

Tested.

[JoanSForgeFlow]

Thank you @MiquelRForgeFlow . Looks good to me

[AaronHForgeFlow]

Code review

[OCA-git-bot]

This PR has the approved label and has been created more than 5 days ago. It should therefore be ready to merge by a maintainer (or a PSC member if the concerned addon has no declared maintainer). 🤖

[github-actions]

There hasn't been any activity on this pull request in the past 4 months, so it has been marked as stale and it will be closed automatically if no further activity occurs in the next 30 days.
If you want this PR to never become stale, please ask a PSC member to apply the "no stale" label.

[JordiMForgeFlow]

@OCA/human-resources-maintainers could we get a review and merge here? :)

[dreispt]

/ocabot merge minor

[OCA-git-bot]

On my way to merge this fine PR!
Prepared branch 16.0-ocabot-merge-pr-151-by-dreispt-bump-minor, awaiting test results.

[OCA-git-bot]

@dreispt your merge command was aborted due to failed check(s), which you can inspect on this commit of 16.0-ocabot-merge-pr-151-by-dreispt-bump-minor.

After fixing the problem, you can re-issue a merge command. Please refrain from merging manually as it will most probably make the target branch red.