R4.0.0

Upgrades docker to use Ubuntu 24.04 (was 22.04) and EPICS 3.15.9 (was 3.15.5). May break everything.

What's Changed

• Bump Ubuntu version in docker to 24.04. by @swh76 in #12
• Adding dependabot to keep reusable actions automatically up to date. by @swh76 in #13
• Bump docker/setup-buildx-action from 1 to 3 by @dependabot[bot] in #16
• Bump actions/checkout from 2 to 6 by @dependabot[bot] in #15
• Bump docker/build-push-action from 2 to 6 by @dependabot[bot] in #14
• Epics3.15.9 by @swh76 in #17

New Contributors

• @dependabot[bot] made their first contribution in #16

Full Changelog: R3.0.3...R4.0.0