Temporarily rename the .ruby-version file to pass CI for rubocop-old

Old versions of rubocop read the ruby version from .ruby-version first.
We made the change upstream which is not captured in versions of
rubocop (< 0.87).

Upstream commit: rubocop/rubocop@02b2c3a

Co-authored-by: Étienne Barrié <etienne.barrie@shopify.com>

spec/erb_lint/linters/rubocop_spec.rb

@@ -32,6 +32,9 @@
   before { linter.run(processed_source) }
 
   context "config is valid when rubocop_config is not explicitly provided" do
+    before(:all) { File.rename(".ruby-version", ".ruby-version.bak") }
+    after(:all) { File.rename(".ruby-version.bak", ".ruby-version") }
+
     let(:linter_config) do
       described_class.config_schema.new(only: ["NotALinter"])
     end
@@ -232,6 +235,9 @@
   end
 
   context "supports config from a provided path" do
+    before(:all) { File.rename(".ruby-version", ".ruby-version.bak") }
+    after(:all) { File.rename(".ruby-version.bak", ".ruby-version") }
+
     after do
       config_file.close
       config_file.unlink