Update fabric_loader_version to v0.16.8 (1.21.2)

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
net.fabricmc:fabric-loader-junit	0.16.7 -> 0.16.8
net.fabricmc:fabric-loader	0.16.7 -> 0.16.8

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