ci: Prevent creating artifact for dynamic ubuntu build

This is not used in the release process anyway, because we are using the static build.

.github/workflows/ci.yaml

@@ -173,7 +173,7 @@ jobs:
             cache: |
               ~/.stack
               .stack-work
-            artifact: postgrest-ubuntu-x64
+            # no artifact for Linux, because we use the static build
 
           - name: MacOS
             runs-on: macos-latest
@@ -210,6 +210,7 @@ jobs:
       - name: Strip Executable
         run: strip result/postgrest*
       - name: Save built executable as artifact
+        if: ${{ matrix.artifact }}
         uses: actions/upload-artifact@v4
         with:
           name: ${{ matrix.artifact }}
@@ -418,11 +419,6 @@ jobs:
           tar cJvf "release-bundle/postgrest-v$VERSION-linux-static-x64.tar.xz" \
             -C artifacts/postgrest-linux-static-x64 postgrest
 
-          # No need to release Ubuntu, as the static Linux binary built with Nix
-          # covers all Linux use-cases
-          #tar cfJv "release-bundle/postgrest-v$VERSION-ubuntu-x64.tar.xz" \
-          #  -C artifacts/postgrest-ubuntu-x64 postgrest
-
           tar cJvf "release-bundle/postgrest-v$VERSION-macos-x64.tar.xz" \
             -C artifacts/postgrest-macos-x64 postgrest