Pin publish workflow to stoolap v0.3.4

CI uses main for development testing. Publish pins to a release
tag — update to v0.3.5 when the stoolap engine release is cut.

Author: semihalev

.github/workflows/publish.yml

@@ -8,7 +8,7 @@ permissions:
   contents: write
 
 env:
-  STOOLAP_VERSION: main
+  STOOLAP_VERSION: v0.3.4
 
 jobs:
   build-lib:
@@ -37,7 +37,7 @@ jobs:
           path: |
             stoolap-engine/target
             ~/.cargo/registry
-          key: rust-${{ matrix.target }}-${{ github.sha }}
+          key: rust-${{ matrix.target }}-${{ env.STOOLAP_VERSION }}
 
       - name: Build libstoolap
         working-directory: stoolap-engine