keyprovider: Pin a specific version of skopeo

The dependency on skopeo is quite fragile as there are several versions
of the project that would generate an encrypted image with a gzip header
that Confidential Containers simply cannot deal with.

For now, let's use f64a376, from Aug 14th 2024 as, empirically, we know
that it works.

We must have tests implemented in order to cover the documentation we
provide, and whether it works or not.

Signed-off-by: Fabiano Fidêncio <fabiano.fidencio@intel.com>

attestation-agent/docker/Dockerfile.keyprovider

@@ -26,7 +26,13 @@ RUN apt-get update && apt-get install -y \
 	pkg-config
 RUN git clone https://github.com/containers/skopeo $GOPATH/src/github.com/containers/skopeo 
 WORKDIR $GOPATH/src/github.com/containers/skopeo
-RUN git checkout v1.14.1
+# The dependency on skopeo is quite fragile as there are several versions of
+# the project that would generate an encrypted image with a gzip header that
+# Confidential Containers simply cannot deal with.
+#
+# For now, let's use f64a376, from Aug 14th 2024 as, empirically, we know that
+# it works.
+RUN git reset --hard f64a376
 ENV DISABLE_DOCS=1
 RUN make bin/skopeo
 RUN make install