fix: replaced days_diff with date_diff for v15 compatibility

[FahidLatheef]

• Latest Develop branch causes Internal Server Error due to incorrect python import.
• It should be date_diff instead of days_diff in frappe.utils.data

[cypress]

lms    Run #962

Run Properties:   Passed #962  •  26a6d7b1cf ℹ️: Merge 0550d3aea366a883ba045f71c6f1b66728357dc3 into eb6b72515e19f66ed493ae9208cb...

Project	lms
Branch Review	fix/days_diff_function_name
Run status	Passed #962
Run duration	00m 29s
Commit	26a6d7b1cf ℹ️: Merge 0550d3aea366a883ba045f71c6f1b66728357dc3 into eb6b72515e19f66ed493ae9208cb...
Committer	Fahid Latheef A
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[pateljannat]

@FahidLatheef It is not a typo. https://github.com/frappe/frappe/blob/develop/frappe/utils/data.py#L333

[FahidLatheef]

@FahidLatheef It is not a typo. https://github.com/frappe/frappe/blob/develop/frappe/utils/data.py#L333

I am using a slightly older patch of Frappe (v15.45.1) and this function doesn't exist. Closing this PR.

[FahidLatheef]

I did more research. This function days_diff doesn't exist in version-15 releases.

https://github.com/frappe/frappe/blob/version-15/frappe/utils/data.py

@pateljannat
Reopening this PR to handle version-15 users.

[frappe-pr-bot]

🎉 This PR is included in version 2.19.0 🎉

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