[build-tools] run resolvePackageManager function in correct directory for custom builds

[szdziedzic]

Why

expo/eas-cli#2401 (comment)

It seems like we are running resolvePackageManager in the wrong directory for custom builds (stepsCtx.global.projectTargetDirectory vs stepsCtx.workingDir).

For standard builds, we run resolvePackageManager in the ctx.getReactNativeProjectDirectory() directory

eas-build/packages/build-tools/src/context.ts

Lines 160 to 162 in b89f2dc

	public get packageManager(): PackageManager {
	return resolvePackageManager(this.getReactNativeProjectDirectory());
	}

that is the default stepsCtx.workingDir for custom builds.

How

Run resolvePackageManager in stepsCtx.workingDir

Test Plan

Tests