Add failing test for trigonometric integral

[StanczakDominik]

References to other Issues or PRs

Test for #20370

Brief description of what is fixed or changed

I added a simple test to integrals/test_failing that compares SymPy's output with the correct output.

Other comments

I'm not 100% sure I shouldn't add a .doit() to the integral.

Release Notes

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#### References to other Issues or PRs

Test for #20370

#### Brief description of what is fixed or changed

I added a simple test to `integrals/test_failing` that compares SymPy's output with the correct output.

#### Other comments

I'm not 100% sure I shouldn't add a `.doit()` to the integral.

#### Release Notes

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[StanczakDominik]

The correct solution is a substitution away from the solution posted in https://math.stackexchange.com/a/1314187/398673 .