Containerfile: Bump the image from Fedora 38 -> 39

The main motivation behind this change is the Go 1.21 version which
isn't available on Fedora 38 but is on Fedora 39.

Resolves: containerbuildsystem#387

Signed-off-by: Erik Skultety <[email protected]>

Containerfile

@@ -1,4 +1,4 @@
-FROM registry.fedoraproject.org/fedora-minimal:38
+FROM registry.fedoraproject.org/fedora-minimal:39
 LABEL maintainer="Red Hat"
 
 WORKDIR /src
@@ -28,4 +28,16 @@ RUN npm install && \
     corepack enable yarn && \
     microdnf -y remove nodejs-npm
 
+# Install an older version of Go fixed at 1.20 (along with the base >=1.21):
+#   - install Go's official shim
+#   - let the shim download the actual Go SDK (the download forces the output parent dir to $HOME)
+#   - move the SDK to a host local install system-wide location
+#   - remove the shim as it forces and expects the SDK to be used from $HOME
+#   - clean any build artifacts Go creates as part of the process.
+RUN go install golang.org/dl/go1.20@latest && \
+    $HOME/go/bin/go1.20 download && \
+    mkdir /usr/local/go && \
+    mv $HOME/sdk/go1.20 /usr/local/go && \
+    rm -rf $HOME/go $HOME/.cache/go-build/
+
 ENTRYPOINT ["cachi2"]