On the contrary, in a star undergoing fusion the conditions may well cause nuclear reactions such as induced fission, making the effective half-life of unstable nuclides shorter than their half-lives when isolated. In the same way that uranium and plutonium in a nuclear reactor are fissioned much faster than their natural half-lives of millions or billions of years. I predict that would mask the effect of gravitational time dilation which has been calculated to be tiny by other answers.

While it's not a heavy nuclide, Lithium-7 is destroyed in fusing stars, and its presence or absence helps distinguish red dwarfs from brown dwarfs.