Go: fixing tests for Go 1.16.

In Go 1.16, the module-aware mode is enabled by default; to fall back to
previous behavior, the GO111MODULE environment variable should be set to
'auto'.

Details: https://golang.org/doc/go1.16

auto/modules/go

@@ -111,7 +111,7 @@ install: ${NXT_GO}-install
 ${NXT_GO}:
 
 ${NXT_GO}-install: ${NXT_GO}-install-src ${NXT_GO}-install-env
-	GOPATH=\$(DESTDIR)\$(GOPATH) ${NXT_GO} build ${NXT_GO_PKG}
+	GOPATH=\$(DESTDIR)\$(GOPATH) GO111MODULE=auto ${NXT_GO} build ${NXT_GO_PKG}
 
 ${NXT_GO}-install-src:
 	install -d \$(DESTDIR)\$(NXT_GO_DST)/src/${NXT_GO_PKG}

test/unit/applications/lang/go.py

@@ -13,6 +13,7 @@ class TestApplicationGo(TestApplicationProto):
         env = os.environ.copy()
         env['GOPATH'] = option.current_dir + '/build/go'
         env['GOCACHE'] = option.cache_dir + '/go'
+        env['GO111MODULE'] = 'auto'
 
         if static:
             args = [

test/unit/check/go.py

@@ -8,6 +8,7 @@ def check_go(current_dir, temp_dir, test_dir):
 
     env = os.environ.copy()
     env['GOPATH'] = current_dir + '/build/go'
+    env['GO111MODULE'] = 'auto'
 
     try:
         process = subprocess.Popen(