fix verify codegen version bump

Author: aajtodd

buildSrc/src/main/kotlin/tasks/VerifyCodegenVersionBump.kt

@@ -55,7 +55,6 @@ open class VerifyCodegenVersionBump : DefaultTask() {
             project.exec {
                 commandLine("git", "diff", "--name-only", effectiveBaseRef, "HEAD", "--", projectName)
                 standardOutput = changesOutput
-                isIgnoreExitValue = true
             }
 
             if (changesOutput.toString().isNotEmpty()) {

tools/ci-scripts/check-codegen-version

@@ -6,4 +6,8 @@
 
 set -eux
 cd smithy-rs
+# GH actions generally does a shallow checkout, we need to fetch the base ref for diffing to work
+BASE_REF="${GITHUB_BASE_REF:=main}"
+echo "fetching base ref $BASE_REF from origin"
+git fetch --no-tags --progress --no-recurse-submodules --depth=1 origin $BASE_REF
 ./gradlew verifyCodegenVersionBump