Rework spellchecking, add lint-spell (#29106)

- 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- Remove inaccurate and outdated info in docs (we do not need GOPATH for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.

docs/content/development/hacking-on-gitea.en-us.md

@@ -243,10 +243,10 @@ documentation using:
 make generate-swagger
 ```
 
-You should validate your generated Swagger file and spell-check it with:
+You should validate your generated Swagger file:
 
 ```bash
-make swagger-validate misspell-check
+make swagger-validate
 ```
 
 You should commit the changed swagger JSON file. The continuous integration

docs/content/development/hacking-on-gitea.zh-cn.md

@@ -228,10 +228,10 @@ Gitea Logo的 PNG 和 SVG 版本是使用 `TAGS="gitea" make generate-images`
 make generate-swagger
 ```
 
-您应该验证生成的 Swagger 文件并使用以下命令对其进行拼写检查：
+您应该验证生成的 Swagger 文件：
 
 ```bash
-make swagger-validate misspell-check
+make swagger-validate
 ```
 
 您应该提交更改后的 swagger JSON 文件。持续集成服务器将使用以下方法检查是否已完成：