.github/workflows/main.yml: fall back to go get instead of go install for installing aux tools

It is unclear why `go install` doesn't work in Github Actions. Needs additional investigation.
The following error is returned now:

cannot find package "golang.org/x/lint/golint" in any of:
	/opt/hostedtoolcache/go/1.15.5/x64/src/golang.org/x/lint/golint (from $GOROOT)
	/home/runner/go/src/golang.org/x/lint/golint (from $GOPATH)

.github/workflows/main.yml

@@ -14,8 +14,8 @@ jobs:
         id: go
       - name: Dependencies
         run: |
-          go install golang.org/x/lint/golint
-          go install github.com/kisielk/errcheck
+          go get -u golang.org/x/lint/golint
+          go get -u github.com/kisielk/errcheck
           curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.29.0
       - name: Code checkout
         uses: actions/checkout@master