Fix issue where test nondeterministically failed if SwiftPM doesn't return build settings quickly

We might not have build settings at the time when we get the first diagnostics notification here and thus might get syntactic fallback diagnostics that don't contain 'Cannot find ... in scope'

Author: ahoppen

Tests/SourceKitLSPTests/PublishDiagnosticsTests.swift

@@ -137,10 +137,14 @@ final class PublishDiagnosticsTests: XCTestCase {
     )
 
     _ = try project.openDocument("FileB.swift")
-    let diagnosticsBeforeChangingFileA = try await project.testClient.nextDiagnosticsNotification()
-    XCTAssert(
-      diagnosticsBeforeChangingFileA.diagnostics.contains(where: { $0.message == "Cannot find 'sayHello' in scope" })
-    )
+    try await repeatUntilExpectedResult {
+      let diagnostics = try await project.testClient.nextDiagnosticsNotification()
+      if diagnostics.diagnostics.contains(where: { $0.message == "Cannot find 'sayHello' in scope" }) {
+        return true
+      }
+      logger.debug("Received unexpected diagnostics: \(diagnostics.forLogging)")
+      return false
+    }
 
     let updatedACode = "func sayHello() {}"
     let aUri = try project.uri(for: "FileA.swift")