github-ci: get rid of set-env in github actions

Seems set-env is deprecated this patch replaces it.
See for details https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/

Following issue should be fixed:
```
Error: Unable to process command '::set-env name=PATH::/Users/runner/work/tuple-merger/tuple-merger/share/bin:/usr/local/opt/pipx_bin:/Users/runner/.cargo/bin:/usr/local/lib/ruby/gems/2.7.0/bin:/usr/local/opt/ruby/bin:/usr/local/opt/curl/bin:/usr/local/bin:/usr/local/sbin:/Users/runner/bin:/Users/runner/.yarn/bin:/usr/local/go/bin:/Users/runner/Library/Android/sdk/tools:/Users/runner/Library/Android/sdk/platform-tools:/Users/runner/Library/Android/sdk/ndk-bundle:/Library/Frameworks/Mono.framework/Versions/Current/Commands:/usr/bin:/bin:/usr/sbin:/sbin:/Users/runner/.dotnet/tools:/Users/runner/.ghcup/bin:/Users/runner/hostedtoolcache/stack/2.5.1/x64' successfully.
Error: The `set-env` command is disabled. Please upgrade to using Environment Files or opt into unsecure command execution by setting the `ACTIONS_ALLOW_UNSECURE_COMMANDS` environment variable to `true`. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/
```

Author: olegrok

.github/workflows/luarocks-build.yml

@@ -65,7 +65,7 @@ jobs:
         run: |
           cd $GITHUB_WORKSPACE/tarantool/build
           cmake --build . --config $BUILD_TYPE --target install -- -j
-          echo "::set-env name=PATH::$GITHUB_WORKSPACE/share/bin:$PATH"
+          echo "PATH=$GITHUB_WORKSPACE/share/bin:$PATH" >> $GITHUB_ENV
 
 
       - name: luarocks make and pack
@@ -92,7 +92,7 @@ jobs:
         shell: bash
         run: |
           brew install make
-          echo "::set-env name=PATH::$(brew --prefix)/opt/make/libexec/gnubin:$PATH"
+          echo "PATH=$(brew --prefix)/opt/make/libexec/gnubin:$PATH" >> $GITHUB_ENV
 
       - name: check examples
         run: |