ci/gha: install latest stable Go version

Jobs verify/compile-buildtags and verify/deps relied on whatever Go
version is available from the Ubuntu-20.04 image, which seems to be
1.15.x).

Job test/cross-i386 was installing whatever Go version is considered to
be the default one by actions/setup-go@v2, which seems to be go 1.15.15
at the moment.

Fix all three jobs to install Go 1.x (which should translate to latest
stable Go version, i.e. 1.17.2 as of now).

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

.github/workflows/test.yml

@@ -119,7 +119,9 @@ jobs:
         sudo apt -q install libseccomp-dev libseccomp-dev:i386 gcc-multilib criu
 
     - name: install go
-      uses: actions/setup-go@v2 # use default Go version
+      uses: actions/setup-go@v2
+      with:
+        go-version: 1.x # Latest stable
 
     - name: unit test
       # cgo is disabled by default when cross-compiling

.github/workflows/validate.yml

@@ -30,6 +30,10 @@ jobs:
       CGO_CFLAGS: -g -O2 -Werror
     steps:
       - uses: actions/checkout@v2
+      - name: install go
+        uses: actions/setup-go@v2
+        with:
+          go-version: 1.x # Latest stable
       - name: compile with no build tags
         run: make BUILDTAGS=""
 
@@ -93,6 +97,10 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
     - uses: actions/checkout@v2
+    - name: install go
+      uses: actions/setup-go@v2
+      with:
+        go-version: 1.x # Latest stable
     - name: cache go mod and $GOCACHE
       uses: actions/cache@v2
       with: