fix: upgrade Go image version to 1.23.4

Dockerfile

@@ -1,12 +1,26 @@
-# Build stage
-FROM golang:1.22-alpine AS builder
+########################
+# — Build stage —
+########################
+FROM golang:1.23.4-alpine AS builder
+
+# git is needed to fetch modules and root CAs
+RUN apk add --no-cache git ca-certificates
+
 WORKDIR /src
-COPY go.* ./
+
+# Copy *both* dependency files first so Docker-layer caching works
+COPY go.mod go.sum ./
 RUN go mod download
+
+# Bring in the rest of the source
 COPY . .
+
+# Build static binary
 RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o /out/action ./main.go
 
-# Runtime Stage
+########################
+# — Runtime stage —
+########################
 FROM alpine:3.20
 COPY --from=builder /out/action /usr/local/bin/action
 ENTRYPOINT ["/usr/local/bin/action"]