Style/CollectionMethods does not detect inject -> reduce in certain cases

[dgollahon]

Expected behavior

[1, 2].inject(:+)     # =>  Style/CollectionMethods: Prefer reduce over inject.
[1, 2].inject(0, :+)  # =>  Style/CollectionMethods: Prefer reduce over inject.
[1, 2].inject(0, &:+) # =>  Style/CollectionMethods: Prefer reduce over inject.

Actual behavior

[1, 2].inject(:+)     # => Nothing is flagged
[1, 2].inject(0, :+)  # => Nothing is flagged
[1, 2].inject(0, &:+) # => Nothing is flagged

Note that the following works correctly:

[1, 2].inject(&:+)                 # => Style/CollectionMethods: Prefer reduce over inject.
[1, 2].inject(0) { |a, b| a + b }  # => Style/CollectionMethods: Prefer reduce over inject.

Steps to reproduce the problem

Add an .inject to some code and run rubocop.

RuboCop version

rubocop -V

warning: parser/current is loading parser/ruby27, which recognizes
warning: 2.7.2-compliant syntax, but you are running 2.7.1.
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.
1.6.1 (using Parser 2.7.2.0, rubocop-ast 1.3.0, running on ruby 2.7.1 x86_64-darwin19)