Bump cfg-expr from 0.15.2 to 0.15.4 (#14808)

Bumps [cfg-expr](https://github.com/EmbarkStudios/cfg-expr) from 0.15.2 to 0.15.4.
- [Release notes](https://github.com/EmbarkStudios/cfg-expr/releases)
- [Changelog](https://github.com/EmbarkStudios/cfg-expr/blob/main/CHANGELOG.md)
- [Commits](EmbarkStudios/cfg-expr@0.15.2...0.15.4)

---
updated-dependencies:
- dependency-name: cfg-expr
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

substrate/Cargo.lock

@@ -17,7 +17,7 @@ proc-macro = true
 [dependencies]
 derive-syn-parse = "0.1.5"
 Inflector = "0.11.4"
-cfg-expr = "0.15.1"
+cfg-expr = "0.15.4"
 itertools = "0.10.3"
 proc-macro2 = "1.0.56"
 quote = "1.0.28"