ci: use a patched sccache on macOS

This version is much less likely to timeout on server startup since it
runs the expensive computation in a background thread.

See https://github.com/mozilla/sccache/pull/868 for the status.

.gitlab/ci/sccache.sh

@@ -2,17 +2,17 @@
 
 set -e
 
-readonly version="0.2.13"
-
 case "$( uname -s )" in
     Linux)
+        version="0.2.13"
         shatool="sha256sum"
         sha256sum="28a5499e340865b08b632306b435913beb590fbd7b49a3f887a623b459fabdeb"
         platform="x86_64-unknown-linux-musl"
         ;;
     Darwin)
+        version="gfe63078"
         shatool="shasum -a 256"
-        sha256sum="f564e948abadfc9e409eb1cd7babf24c6784057d5506c3b0a04cdd37cd830ae9"
+        sha256sum="60a0302b1d7227f7ef56abd82266353f570d27c6e850c56c6448bf62def38888"
         platform="x86_64-apple-darwin"
         ;;
     *)
@@ -20,6 +20,7 @@ case "$( uname -s )" in
         exit 1
         ;;
 esac
+readonly version
 readonly shatool
 readonly sha256sum
 readonly platform
@@ -27,10 +28,17 @@ readonly platform
 readonly filename="sccache-$version-$platform"
 readonly tarball="$filename.tar.gz"
 
+if [ "$( uname -s )" = "Darwin" ]; then
+    url="https://paraview.org/files/dependencies"
+else
+    url="https://github.com/mozilla/sccache/releases/download/$version"
+fi
+readonly url
+
 cd .gitlab
 
 echo "$sha256sum  $tarball" > sccache.sha256sum
-curl -OL "https://github.com/mozilla/sccache/releases/download/$version/$tarball"
+curl -OL "$url/$tarball"
 $shatool --check sccache.sha256sum
 tar xf "$tarball"
 mv "$filename/sccache" .