Rework spellchecking, add lint-spell (#29112)

Backport clean cherry-picks of
https://github.com/go-gitea/gitea/commit/9c39f8515fa88d644736c6773d7a05d070a02e82
and
https://github.com/go-gitea/gitea/commit/c7a21cbb0c5f8302495fa24baf218dc3462de2c5
onto 1.21.

- Use maintained fork https://github.com/golangci/misspell
- Rename `mispell-check` to `lint-spell`, add `lint-spell-fix`
- Run `lint-spell` in separate actions step
- Lint more files, fix discovered issues
- Remove inaccurate and outdated info in docs (we do not need GOPATH for
tools anymore)

Maybe later we can add more spellchecking tools, but I have not found
any good ones yet.

templates/repo/branch_dropdown.tmpl

@@ -1,7 +1,7 @@
 {{/* Attributes:
 * root
 * ContainerClasses
-* (TODO: search "branch_dropdown" in the template direcotry)
+* (TODO: search "branch_dropdown" in the template directory)
 */}}
 {{$defaultSelectedRefName := $.root.BranchName}}
 {{if and .root.IsViewTag (not .noTag)}}

templates/repo/issue/view_content/comments.tmpl

@@ -367,7 +367,7 @@
 				<div class="timeline-item event">
 					{{if .OriginalAuthor}}
 					{{else}}
-					{{/* Some timeline avatars need a offset to correctly allign with their speech
+					{{/* Some timeline avatars need a offset to correctly align with their speech
 							bubble. The condition depends on review type and for positive reviews whether
 							there is a comment element or not */}}
 					<a class="timeline-avatar{{if or (and (eq .Review.Type 1) (or .Content .Attachments)) (and (eq .Review.Type 2) (or .Content .Attachments)) (eq .Review.Type 3)}} timeline-avatar-offset{{end}}"{{if gt .Poster.ID 0}} href="{{.Poster.HomeLink}}"{{end}}>