add Dockerfile to pre-install mage

.forgejo/actions/tests/Dockerfile

@@ -0,0 +1,14 @@
+# syntax=docker/dockerfile:1
+FROM golang:1.23.0 AS builder
+
+RUN git clone https://github.com/magefile/mage \
+    && cd mage \
+    && git checkout v1.15.0 \
+    && go run bootstrap.go
+
+
+FROM golang:1.23.0-alpine
+
+COPY --from=builder /go/bin/mage /go/bin/mage
+
+ENTRYPOINT ["mage"]

.forgejo/actions/tests/action.yaml

@@ -3,9 +3,9 @@ name: "Testing"
 description: "Performs unit and lint tests for Enbas with mage"
 runs:
   using: "docker"
-  image: "docker://golang:1.23.0-alpine"
+  image: "Dockerfile"
   env:
     ENBAS_TEST_VERBOSE: "1"
     ENBAS_TEST_COVER: "1"
   pre-entrypoint: "go version"
-  entrypoint: "go run magefiles/main.go -v test"
+  entrypoint: "mage -v test"