[Fix #8005] Always inspect anonymous sources

[eugeneius]

Fixes #8005.

When using the expect_offense and expect_no_offenses spec helpers, the processed source is given the special filename "(string)", unless a mock filename is passed as its second argument.

Since #7970, the default configuration for the cop under test is loaded when using the config shared context. If this configuration features an Include key, expect_offense won't work unless a matching mock filename is specified.

Instead of forcing specs for cops with a default Include configuration to do that, I think we can always inspect anonymous sources.

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[koic]

Brilliant! Thank you so much!