chore: don't test tools with earliest (#6589)

Our tools are only expected to run with the latest go version we
support. So for those directories skip running tests on old Go
versions.

internal/kokoro/continuous.sh

@@ -79,8 +79,14 @@ try3 go mod download
 # runDirectoryTests runs all tests in the current directory.
 # If a PATH argument is specified, it runs `go test [PATH]`.
 runDirectoryTests() {
-  go test -race -v -timeout 45m "${1:-./...}" 2>&1 \
-    | tee sponge_log.log
+  if [[ $PWD != *"/internal/"* ]] ||
+    [[ $PWD != *"/third_party/"* ]] &&
+    [[ $KOKORO_JOB_NAME == *"earliest"* ]]; then
+    # internal tools only expected to work with latest go version
+    return
+  fi
+  go test -race -v -timeout 45m "${1:-./...}" 2>&1 |
+    tee sponge_log.log
   # Takes the kokoro output log (raw stdout) and creates a machine-parseable
   # xUnit XML file.
   cat sponge_log.log \

internal/kokoro/presubmit.sh

@@ -49,6 +49,13 @@ exit_code=0
 # Run tests in the current directory and tee output to log file,
 # to be pushed to GCS as artifact.
 runPresubmitTests() {
+  if [[ $PWD != *"/internal/"* ]] ||
+    [[ $PWD != *"/third_party/"* ]] &&
+    [[ $KOKORO_JOB_NAME == *"earliest"* ]]; then
+    # internal tools only expected to work with latest go version
+    return
+  fi
+
   if [ -z ${RUN_INTEGRATION_TESTS} ]; then
     go test -race -v -timeout 15m -short ./... 2>&1 |
       tee sponge_log.log
@@ -67,9 +74,6 @@ runPresubmitTests() {
     go-junit-report -set-exit-code >sponge_log.xml
   # Add the exit codes together so we exit non-zero if any module fails.
   exit_code=$(($exit_code + $?))
-  # There are some types of build failures that go-junit-report does not
-  # properly handle. We can be safe here and run go build as well to catch such
-  # failures.
   if [[ $PWD != *"/internal/"* ]]; then
     go build ./...
   fi