Bump alpine from 3.20.3 to 3.21.0 in /cmd/scanner

Bumps alpine from 3.20.3 to 3.21.0.

---
updated-dependencies:
- dependency-name: alpine
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

cmd/scanner/Dockerfile

@@ -8,12 +8,12 @@ WORKDIR /go/src/github.com/artifacthub/scanner/cmd/scanner
 RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o /scanner .
 
 # Trivy installer
-FROM alpine:3.20.3 AS trivy-installer
+FROM alpine:3.21.0 AS trivy-installer
 RUN apk --no-cache add curl
 RUN curl -sfL https://raw.githubusercontent.com/aquasecurity/trivy/main/contrib/install.sh | sh -s -- -b /usr/local/bin v0.56.1
 
 # Final stage
-FROM alpine:3.20.3
+FROM alpine:3.21.0
 RUN apk --no-cache add ca-certificates && addgroup -S scanner -g 1000 && adduser -S scanner -u 1000 -G scanner
 USER 1000
 WORKDIR /home/scanner