chore(internal/kokoro): skip submodules repeated test if root directoy is already pushd

[rahul2393]

In #10251 there are repeated tests which internal/kokoro/presubmit.sh bash script was running.

Example:

CHANGED_DIRS='.
aiplatform
dlp
internal
managedkafka
spanner
video'

will run test twice for spanner once with "pushd ./spanner" and other with "pushd spanner"

We don't really need to run the sub-directories test if changes were detected in root directory(".") since it will anyways run all the tests in submodules.

[noahdietz]

I'm not sure a change to a file in the top-dir (e.g. doc.go) should trigger tests in all submodules. This is a good call out though, I think we need to instead run tests in . directly but not ./... from the top, if that makes sense e.g. go test .. There are no tests in the top but I suppose it will still build the code...WDYT?

[codyoss]

./... is a module aware command and should only run in the scope of a module

[rahul2393]

@codyoss Thanks, can you please help find why did it ran tests twice on submodules? https://btx.cloud.google.com/invocations/de35c87c-677f-4eb7-9a48-4a7e77a94952/targets/cloud-devrel%2Fclient-libraries%2Fgo%2Fgoogle-cloud-go%2Fpresubmit%2Fearliest-version/log (I found the reason, in next comment)

[rahul2393]

find "$d" -name go.mod
is returning all the submodules, example output of find "." -name go.mod

./dataflow/go.mod
./maps/go.mod
./resourcemanager/go.mod
./essentialcontacts/go.mod
./commerce/go.mod
./orgpolicy/go.mod
./workstations/go.mod
./webrisk/go.mod
./datastream/go.mod
./binaryauthorization/go.mod
./servicehealth/go.mod
./apigeeregistry/go.mod
./beyondcorp/go.mod
./kms/go.mod
./confidentialcomputing/go.mod
./resourcesettings/go.mod
./video/go.mod
./netapp/go.mod
./aiplatform/go.mod
./discoveryengine/go.mod
./go.mod
./servicemanagement/go.mod
./shopping/go.mod
./domains/go.mod
./vpcaccess/go.mod
./trace/go.mod
./bigtable/go.mod
./oslogin/go.mod
./gkehub/go.mod
./securityposture/go.mod
./gkeconnect/go.mod
./networkmanagement/go.mod
./identitytoolkit/go.mod
./asset/go.mod
./securitycenter/go.mod
./chat/go.mod
./apphub/go.mod
./dialogflow/go.mod
./storageinsights/go.mod
./rapidmigrationassessment/go.mod
./documentai/go.mod
...

Hence the issue