multiboot2: v0.15.0

What's Changed

• ci: refactoring: less code duplication by @phip1611 in #125
• ci: cache per rust version by @phip1611 in #126
• multiboot2: Allow to get Custom Tags by @phip1611 in #118
• multiboot2-v0.15 by @phip1611 in #122

Full Changelog: multiboot2-v0.14.2...multiboot2-v0.15.0