Handle non-Symbol args in TryConvertMut for time Offset

[lopopolo]

it looks like we need to handle non-Symbol args in the same way:

[3.1.2] > Time.at(12, 'in' => 'Z')
<internal:timev>:270:in `at': unknown keyword: "in" (ArgumentError)
        from (irb):1:in `<main>'
        from /usr/local/var/rbenv/versions/3.1.2/lib/ruby/gems/3.1.0/gems/irb-1.4.1/exe/irb:11:in `<top (required)>'
        from /usr/local/var/rbenv/versions/3.1.2/bin/irb:25:in `load'
        from /usr/local/var/rbenv/versions/3.1.2/bin/irb:25:in `<main>'
[3.1.2] > Time.at(12, Object.new => 'Z')
<internal:timev>:270:in `at': unknown keyword: #<Object:0x00000001091c7d70> (ArgumentError)
        from (irb):2:in `<main>'
        from /usr/local/var/rbenv/versions/3.1.2/lib/ruby/gems/3.1.0/gems/irb-1.4.1/exe/irb:11:in `<top (required)>'
        from /usr/local/var/rbenv/versions/3.1.2/bin/irb:25:in `load'
        from /usr/local/var/rbenv/versions/3.1.2/bin/irb:25:in `<main>'

Originally posted by @lopopolo in #1956 (comment)

[lopopolo]

This ticket is related to #2091.