[ci] use go mod instead of go get in spec.bats

[lifubang]

When we run integration test in go 1.22, it got an error:

 ✗ spec validator
   (in test file tests/integration/spec.bats, line 37)
     `GO111MODULE=auto go get github.com/xeipuuv/gojsonschema' failed
   runc spec (status=0):
   
   Cloning into 'runtime-spec'...
   HEAD is now at 36852b0 version: release v1.2.0
   go: go.mod file not found in current directory or any parent directory.
        'go get' is no longer supported outside a module.
        To build and install a command, use 'go install' with a version,
        like 'go install example.com/cmd@latest'
        For more information, see https://golang.org/doc/go-get-install-deprecation
        or run 'go help get' or 'go help install'.

Although we have not supported go 1.22 yet, but I think we should update the spec.bat first.

[kolyshkin]

Maybe easier to do

./validate config-schema.json ../../config.json

(and remove cd and SCHEMA= above)

Long term, I guess, we need to fix runtime-spec to

• embed config-schema.json into validate binary
• add go.mod to runtime-spec
• make it easier to use so go install github.com/opencontainers/runtime-spec/schema/validate@$SPEC_REF results in validate binary ready to be used.

[kolyshkin]

LGTM