build(deps): update capnp requirement from 0.14.0 to 0.15.2 in /gst-depth-meta-rs

Updates the requirements on capnp to permit the latest version.

Commits

• 8d37d59 fix formatting
• aed3f71 prepare for capnp-v0.15.2 release
• e7ee0ef remove pointer munging and add test
• 89f9e52 prepare for capnp-v0.15.1 release
• 2be9ac4 Merge pull request #356 from punkeel/punkeel/msrv
• ae314cd Specify the minimum supported Rust version for capnp crate
• ae167e5 Merge pull request #354 from danieleades/clippy/use-self
• dd4e923 use 'Self' keyword to refer to own type
• 8ead5d3 add test coverage for pipelining with groups
• 8f1cad4 Merge pull request #345 from danieleades/use-of-ref
• Additional commits viewable in compare view