ci/gha: remove stable: when installing Go

Since the recent bump of actions/setup-go to v3 (commit
9d2268b9db), specifying "stable:" is no longer needed
when we want to try a beta or rc version of Go.

Remove it.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

.github/workflows/test.yml

@@ -62,7 +62,6 @@ jobs:
     - name: install go ${{ matrix.go-version }}
       uses: actions/setup-go@v3
       with:
-        stable: '!contains(${{ matrix.go-version }}, "beta") && !contains(${{ matrix.go-version }}, "rc")'
         go-version: ${{ matrix.go-version }}
 
     - name: build