Bump tracing-subscriber from 0.3.19 to 0.3.20 in /demos/vc_issuer (#3457)

Bumps [tracing-subscriber](https://github.com/tokio-rs/tracing) from 0.3.19 to 0.3.20.
- [Release notes](https://github.com/tokio-rs/tracing/releases)
- [Commits](tokio-rs/tracing@tracing-subscriber-0.3.19...tracing-subscriber-0.3.20)

---
updated-dependencies:
- dependency-name: tracing-subscriber
  dependency-version: 0.3.20
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]