Update ghost

Changes:

- https://github.com/docker-library/ghost/commit/b0a55c8: Update to 4.20.4, ghost-cli 1.17.4

library/ghost

@@ -4,14 +4,14 @@ Maintainers: Tianon Gravi <[email protected]> (@tianon),
              Joseph Ferguson <[email protected]> (@yosifkit)
 GitRepo: https://github.com/docker-library/ghost.git
 
-Tags: 4.20.3, 4.20, 4, latest
+Tags: 4.20.4, 4.20, 4, latest
 Architectures: amd64, arm32v7, arm64v8, ppc64le, s390x
-GitCommit: 5747e66284f94ecfdc67695c79ab62bd5ac8d456
+GitCommit: b0a55c8c18a1f81ef8714caf56b5120e6d362ed0
 Directory: 4/debian
 
-Tags: 4.20.3-alpine, 4.20-alpine, 4-alpine, alpine
+Tags: 4.20.4-alpine, 4.20-alpine, 4-alpine, alpine
 Architectures: amd64, arm32v6, arm32v7, arm64v8
-GitCommit: 5747e66284f94ecfdc67695c79ab62bd5ac8d456
+GitCommit: b0a55c8c18a1f81ef8714caf56b5120e6d362ed0
 Directory: 4/alpine
 
 Tags: 3.42.6, 3.42, 3