releaser: Fix regexp

releaser: Fix regexp

Original regexp used a char class which caused the regexp to only
check 1 symbol instead of a substring like "See" and "Closes".
So it would match `e #x` instead of `See #x` and many other
weird combinations.

Tests were passing as they never checked against an input that
would confuse that regexp.

Found with go-critic static analyzer, `badRegexp` checker.