Fix yarn install command on PackageHub

Author: olafurpg

packagehub/src/main/scala/com/sourcegraph/packagehub/PackageActor.scala

@@ -247,7 +247,10 @@ class PackageActor(
       return dump
     pkg match {
       case _: NpmPackage =>
-        exec(sourceroot, List("yarn", "install"))
+        val toolVersions = sourceroot.resolve(".tool-versions")
+        if (!Files.isRegularFile(toolVersions)) {
+          Files.write(toolVersions, List("yarn 1.22.4").asJava)
+        }
         val tsconfig = sourceroot.resolve("tsconfig.json")
         if (!Files.isRegularFile(tsconfig)) {
           val config = Obj(
@@ -256,6 +259,7 @@ class PackageActor(
           )
           Files.write(tsconfig, List(ujson.write(config, indent = 2)).asJava)
         }
+        exec(sourceroot, List("yarn", "install"))
         exec(
           sourceroot,
           List("npx", "@olafurpg/lsif-tsc", "-p", sourceroot.toString)