Redirect to previous page when cancelling new deadline deviation

[ihalaij1]

Description

What?

Previously, the cancel button always sent the user to the deadline deviation list page. Now, it sends the user to the page where they came from, if possible.

Why?

This was requested by a teacher.

Fixes #1278

What type of test did you run?

• [ ] Accessibility test using the WAVE extension.
• [ ] Django unit tests.
• [ ] Selenium tests.
• [ ] Other test. (Add a description below)
• [x] Manual testing.

Tested that redirection works after cancelling new deadline deviation on inspect submission page and user results page.

Did you test the changes in

• [x] Chrome
• [ ] Firefox
• [ ] This pull request cannot be tested in the browser.

Translation

• [ ] Did you modify or add new strings in the user interface? (Read about how to create translation)

Programming style

• [x] Did you follow our style guides?
• [x] Did you use Python type hinting in all functions that you added or edited? (type hints for function parameters and return values)

Have you updated the README or other relevant documentation?

• [ ] documents inside the doc directory.
• [ ] README.md.
• [ ] Aplus Manual.
• [ ] Other documentation (mention below which documentation).

Is it Done?

• [ ] Reviewer has finished the code review
• [ ] After the review, the developer has made changes accordingly
• [ ] Customer/Teacher has accepted the implementation of the feature

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