http: check for "Host:" case insensitively

When checking if the user wants to replace the header, the check should
be case insensitive.

Adding test 461 to verify

Found-

http: check for "Host:" case insensitively

When checking if the user wants to replace the header, the check should
be case insensitive.

Adding test 461 to verify

Found-by: Dan Fandrich
Ref: #12782
Closes #12784

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