fix: remove non use GIT_TAG

Author: guitarrapc

.github/workflows/build-release.yml

@@ -88,8 +88,6 @@ jobs:
       - uses: actions/setup-dotnet@v1
         with:
           dotnet-version: "${{ env.DOTNET_SDK_VERSION_3 }}"
-      # set release tag(*.*.*) to env.GIT_TAG
-      - run: echo "GIT_TAG=${GITHUB_REF#refs/tags/}" >> $GITHUB_ENV
       - run: dotnet build src/ZString -c Release -p:Version=${{ env.GIT_TAG }}
       - run: dotnet test tests/ZString.Tests -c Release --no-build
       - run: dotnet pack ./src/ZString/ZString.csproj -c Release --no-build -p:Version=${{ env.GIT_TAG }} -o ./publish