Fix kwargs deprecation warnings in git diff specs

This commit fixes warnings like:

Passing the keyword argument as the last hash parameter is deprecated

spec/lib/gitlab/git/diff_spec.rb

@@ -301,19 +301,19 @@ EOT
 
   describe '#too_large?' do
     it 'returns true for a diff that is too large' do
-      diff = described_class.new(diff: 'a' * 204800)
+      diff = described_class.new({ diff: 'a' * 204800 })
 
       expect(diff.too_large?).to eq(true)
     end
 
     it 'returns false for a diff that is small enough' do
-      diff = described_class.new(diff: 'a')
+      diff = described_class.new({ diff: 'a' })
 
       expect(diff.too_large?).to eq(false)
     end
 
     it 'returns true for a diff that was explicitly marked as being too large' do
-      diff = described_class.new(diff: 'a')
+      diff = described_class.new({ diff: 'a' })
 
       diff.too_large!
 
@@ -323,19 +323,19 @@ EOT
 
   describe '#collapsed?' do
     it 'returns false by default even on quite big diff' do
-      diff = described_class.new(diff: 'a' * 20480)
+      diff = described_class.new({ diff: 'a' * 20480 })
 
       expect(diff).not_to be_collapsed
     end
 
     it 'returns false by default for a diff that is small enough' do
-      diff = described_class.new(diff: 'a')
+      diff = described_class.new({ diff: 'a' })
 
       expect(diff).not_to be_collapsed
     end
 
     it 'returns true for a diff that was explicitly marked as being collapsed' do
-      diff = described_class.new(diff: 'a')
+      diff = described_class.new({ diff: 'a' })
 
       diff.collapse!
 
@@ -359,7 +359,7 @@ EOT
 
   describe '#collapse!' do
     it 'prunes the diff' do
-      diff = described_class.new(diff: "foo\nbar")
+      diff = described_class.new({ diff: "foo\nbar" })
 
       diff.collapse!