Don’t update Package.resolved from sourcekit-lsp

`SwiftPMWorkspace.reloadPackage` called `loadPackageGraph`, which causes package resolution and could thus update `Package.resolved`. This caused race conditions when `swift package update` was run from terminal while sourcekit-lsp is running since sourcekit-lsp was notified about the file changes and thus reloaded the pacakge to get build settings for the modified files.

Set `forceResolvedVersions` to only resolve packages based on the versions in `Package.resolved`, eliminating this problem.

Fixes apple#707
rdar://105173375

Sources/SKSwiftPMWorkspace/SwiftPMWorkspace.swift

@@ -177,6 +177,7 @@ extension SwiftPMWorkspace {
 
     let packageGraph = try self.workspace.loadPackageGraph(
       rootInput: PackageGraphRootInput(packages: [packageRoot]),
+      forceResolvedVersions: true,
       observabilityScope: observabilitySystem.topScope
     )