fix distDocker - revert gradle change to providers.exec

[macfarla]

PR description

distDocker was only creating evmtool docker not besu docker image

it affects CI as well - no longer publishing docker for besu: https://hub.docker.com/r/hyperledger/besu/tags (last develop was 5 days ago)

Seems to have been broken by this commit -
1508b5c#diff-49a96e7eea8a94af862798a45174e6ac43eb4f8b4bd40759b5da63ba31ec3ef7

This PR reverts one change from #8295

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• Considered documentation and added the doc-change-required label to this PR if updates are required.
• Considered the changelog and included an update if required.
• For database changes (e.g. KeyValueSegmentIdentifier) considered compatibility and performed forwards and backwards compatibility tests

Locally, you can run these tests to catch failures early:

• spotless: ./gradlew spotlessApply
• unit tests: ./gradlew build
• acceptance tests: ./gradlew acceptanceTest
• integration tests: ./gradlew integrationTest
• reference tests: ./gradlew ethereum:referenceTests:referenceTests

[siladu]

LGTM