Update dependency ts-jest to v26.5.6

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
ts-jest (source)	26.5.4 -> 26.5.6

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Release Notes

kulshekhar/ts-jest

### [`v26.5.6`](https://togithub.com/kulshekhar/ts-jest/blob/master/CHANGELOG.md#​2656-httpsgithubcomkulshekharts-jestcomparev2655v2656-2021-05-05) [Compare Source](https://togithub.com/kulshekhar/ts-jest/compare/v26.5.5...v26.5.6) ##### Code Refactoring - refactor(config): show warning message for `sourceMap: false` ([#​2557](https://togithub.com/kulshekhar/ts-jest/pull/2557)) ([cf60990](https://togithub.com/kulshekhar/ts-jest/commit/cf609900e2c5937755123bd08ca2c5f2ff5e0651)). ### [`v26.5.5`](https://togithub.com/kulshekhar/ts-jest/blob/master/CHANGELOG.md#​2655-httpsgithubcomkulshekharts-jestcomparev2654v2655-2021-04-15) [Compare Source](https://togithub.com/kulshekhar/ts-jest/compare/v26.5.4...v26.5.5) ##### Bug Fixes - **compiler:** return file content on emitSkipped for non ts/tsx files ([#​2515](https://togithub.com/kulshekhar/ts-jest/issues/2515)) ([0320fb3](https://togithub.com/kulshekhar/ts-jest/commit/0320fb3ac22056aafe4d7ae966eab84dbf23fda9)), closes [#​2513](https://togithub.com/kulshekhar/ts-jest/issues/2513)

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