gatsby-source-contentful fails with "EMFILE: too many open files" on Vercel

[xmflsct]

Description

Related to #12011, but with Contentful. It was fine until I add more content on Contentful.

contentTypes fetched 15
Updated entries  1594
Updated assets  2562

Tried graceful-fs and fs-extra with no luck.

Note, the reason of using lower version of gatsby-source-contentful is related to #22792.

Steps to reproduce

Deploy using Vercel.

Expected result

Build successful.

Actual result

Too many files opened.

Environment

  Binaries:
    Node: 12.16.2 - /usr/local/opt/node@12/bin/node
    Yarn: 1.22.4 - /usr/local/bin/yarn
    npm: 6.14.4 - /usr/local/opt/node@12/bin/npm
  npmPackages:
    gatsby: ^2.20.31 => 2.20.31 
    gatsby-image: ^2.3.5 => 2.3.5 
    gatsby-plugin-layout: ^1.2.4 => 1.2.4 
    gatsby-plugin-lodash: ^3.2.4 => 3.2.4 
    gatsby-plugin-preact: ^3.2.4 => 3.2.4 
    gatsby-plugin-prefetch-google-fonts: ^1.4.3 => 1.4.3 
    gatsby-plugin-react-helmet: ^3.2.5 => 3.2.5 
    gatsby-plugin-sass: ^2.2.4 => 2.2.4 
    gatsby-plugin-sharp: ^2.5.7 => 2.5.7 
    gatsby-source-contentful: ~2.1.88 => 2.1.100 
    gatsby-source-filesystem: ^2.2.5 => 2.2.5 
    gatsby-transformer-sharp: ^2.4.7 => 2.4.7 
  npmGlobalPackages:
    gatsby-cli: 2.11.17

[xmflsct]

#12011 (comment) method works for me!