Update dependency ts-jest to v26.4.1

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
ts-jest (source)	devDependencies	patch	26.4.0 -> 26.4.1

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Release Notes

kulshekhar/ts-jest

### [`v26.4.1`](https://togithub.com/kulshekhar/ts-jest/blob/master/CHANGELOG.md#​2641-httpsgithubcomkulshekharts-jestcomparev2640v2641-2020-09-29) [Compare Source](https://togithub.com/kulshekhar/ts-jest/compare/v26.4.0...v26.4.1) ##### Bug Fixes - **utils:** `MaybeMockedConstructor` returns T ([#​1976](https://togithub.com/kulshekhar/ts-jest/issues/1976)) ([b7712b2](https://togithub.com/kulshekhar/ts-jest/commit/b7712b2055d8f32dd97999de1d94e8f3515d79e8)) - **utils:** revert `path.join` and add check on prefix ends with `/` ([#​1989](https://togithub.com/kulshekhar/ts-jest/issues/1989)) ([3d9035b](https://togithub.com/kulshekhar/ts-jest/commit/3d9035bd70dc087d4c5a943bb2fe2af2d0822875)), closes [#​1982](https://togithub.com/kulshekhar/ts-jest/issues/1982)

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