chore(deps): update plugin com.github.johnrengelman.shadow to v8

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
com.github.johnrengelman.shadow	7.1.2 -> 8.1.1

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Unit Test Results

0 files   - 3  0 suites   - 3   0s ⏱️ ±0s
0 tests  - 3  0 ✔️ ±0  0 💤 ±0  0 ❌  - 3 

Results for commit 840df9a. ± Comparison against base commit 3a4060d.

This pull request removes 3 tests.

net.silthus.template.TemplatePluginTests ‑ shouldFirePlayerJoinEvent()
net.silthus.template.commands.TemplateCommandsTests ‑ info_forSelf_printsOwnPlayerName()
net.silthus.template.integrations.vault.VaultProviderTest ‑ getPlayerBalance_returnsVaultBalance()

♻️ This comment has been updated with latest results.