RFR: 8072: Bump some maven plugins and fix warnings [v2]

[Christoph Langer]

> Current maven build of JMC core shows some warnings/validation errors that can be fixed by bumping plugin versions.

Christoph Langer has updated the pull request incrementally with one additional commit since the last revision:

  Find a better spotless version

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Changes:
  - all: https://git.openjdk.org/jmc/pull/486/files
  - new: https://git.openjdk.org/jmc/pull/486/files/d14f2d75..9970f9f4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jmc&pr=486&range=01
 - incr: https://webrevs.openjdk.org/?repo=jmc&pr=486&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jmc/pull/486.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/486/head:pull/486

PR: https://git.openjdk.org/jmc/pull/486