Text duplication fix

[tsmethurst]

Closes #134

From matrix conversation:

The problem was exactly here: https://github.com/superseriousbusiness/gotosocial/blob/main/internal/text/common.go#L62

Instead of returning in if no matching tags are found, it should return match.

So basically what happened in that function was that the hashtagfinderregex matched #Hashtag in the string, then it started iterating through the list of tags looking for the replacement... HOWEVER, tag.Name was automatically lowercased by some of the text parsing functionality from earlier

which means that strings.TrimSpace(match) == fmt.Sprintf("#%s", tag.Name) was not true

so the fallback behavior was to return in, which is the whole status

so #Hashtag was being replaced by ALL of in

so the two fixes are to:

1. make that match case insensitive using strings.EqualFold instead of ==
2. return match instead of in so nothing is replaced in case a tag can't be found