Add generateBuildEnvironmentConstants as a dependency of `sourcesJa…

…r` (#4005)

## Motivation and Context
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Fixes #3949 

## Description
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## Testing
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## Checklist
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- [ ] For changes to the smithy-rs codegen or runtime crates, I have
created a changelog entry Markdown file in the `.changelog` directory,
specifying "client," "server," or both in the `applies_to` key.
- [ ] For changes to the AWS SDK, generated SDK code, or SDK runtime
crates, I have created a changelog entry Markdown file in the
`.changelog` directory, specifying "aws-sdk-rust" in the `applies_to`
key.

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codegen-core/build.gradle.kts

@@ -186,6 +186,7 @@ val sourcesJar by tasks.creating(Jar::class) {
     group = "publishing"
     description = "Assembles Kotlin sources jar"
     archiveClassifier.set("sources")
+    dependsOn("generateBuildEnvironmentConstants")
     from(sourceSets.getByName("main").allSource)
 }