chore(internal/librariangen): update gapic-generator-go to v0.54.0

[jskeet]

No description provided.

[quartzmo]

The 0.54.0 version has still not appeared in package docs: https://pkg.go.dev/github.com/googleapis/gapic-generator-go?tab=versions

But I have downloaded it successfully with go get:

$  go get github.com/googleapis/gapic-generator-go@latest
go: downloading github.com/googleapis/gapic-generator-go v0.54.0
go: added github.com/googleapis/gapic-generator-go v0.54.0
go: upgraded golang.org/x/crypto v0.37.0 => v0.38.0
go: upgraded golang.org/x/net v0.39.0 => v0.40.0
go: upgraded golang.org/x/sync v0.13.0 => v0.14.0
go: upgraded golang.org/x/sys v0.32.0 => v0.33.0
go: upgraded golang.org/x/text v0.24.0 => v0.25.0
go: upgraded google.golang.org/genproto v0.0.0-20250414145226-207652e42e2e => v0.0.0-20250519155744-55703ea1f237
go: upgraded google.golang.org/genproto/googleapis/api v0.0.0-20250414145226-207652e42e2e => v0.0.0-20250519155744-55703ea1f237
go: upgraded google.golang.org/genproto/googleapis/rpc v0.0.0-20250414145226-207652e42e2e => v0.0.0-20250519155744-55703ea1f237
go: upgraded google.golang.org/grpc v1.71.1 => v1.72.1

[jskeet]

It's now in the package docs, and I've checked that it works in the container. The changes only affect KMS, Secret Manager and Storage, none of which have been migrated yet, so there's nothing urgent in terms of updating the container used by automation just yet. Merging.