fix(core): don't fail on skipped optional deps, when calculating depsRequiringBuild (#8404)

.changeset/brave-pants-drive.md

@@ -0,0 +1,5 @@
+---
+"@pnpm/core": patch
+---
+
+Don't fail on skipped optional dependencies, when searching for dependencies that should be built.

pkg-manager/core/src/install/index.ts

@@ -1420,7 +1420,7 @@ const _installInContext: InstallFunction = async (projects, ctx, opts) => {
   const depsRequiringBuild: DepPath[] = []
   if (opts.returnListOfDepsRequiringBuild) {
     await Promise.all(Object.entries(dependenciesGraph).map(async ([depPath, node]) => {
-      if (node == null) return // We cannot detect if a skipped optional dependency requires build
+      if (node?.fetching == null) return // We cannot detect if a skipped optional dependency requires build
       const { files } = await node.fetching()
       if (files.requiresBuild) {
         depsRequiringBuild.push(depPath as DepPath)