Custom patterns for GHES 3.7 and below don't support anchors - we should communicate that

[aegilops]

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For patterns we have defined that use anchors in the additional matches, we need to communicate that GitHub Enterprise server v 3.7 and below do not support anchors.

Those additional matches can either be used without anchors (which will sometimes work, but often not) or not used at all (reducing the accuracy/precision of the pattern).