Update dependency ts-jest to v26.4.0

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
ts-jest (source)	devDependencies	minor	26.3.0 -> 26.4.0

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Release Notes

kulshekhar/ts-jest

v26.4.0

Compare Source

Bug Fixes

• utils: pathsToModuleNameMapper resolve path mapping with path.join (#​1969) (81fce4c), closes #​1968
• set minimum jest-util version at 26.1.0 (#​1914) (f00414c), closes #​1913

Features

• config: allow custom options in custom transformers (#​1966) (1452ce4), closes #​1942
• transformers: support hoisting when using @jest/globals (#​1937) (0e5be15), closes #​1593
• transformers: add path-mapping custom AST transformer (#​1927) (3325186)

Performance Improvements

• compiler: remove createProgram for isolatedModules: true to boost startup speed (#​1941) (dd84534)

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