[META] Use correct language for .tmpl

- Upstream chosen `Handlebars` as language for the templates, presumenly
because Github doesn't have an syntax highlighter for Go.
- Forgejo does have syntax highlighting support for Go templates, so use that.

(cherry picked from commit a79718522dc432e32cf322498ddf22ec570fa8fd)
(cherry picked from commit 380d847e5cdb179292c7bd1a5e3e6839fb8b31dd)
(cherry picked from commit 4126a9672d93fc33b72fb816a404056aac64dfc8)
(cherry picked from commit afde0ed82271df540348953a811a8e9db1a83343)
(cherry picked from commit 6ddaca00615340958e1aecca2c4807e39a2b1eff)
(cherry picked from commit 454b2f6b35c018cc631dd8847ae9d3243d9adc37)
(cherry picked from commit 58c10e1f93da8d8f193936eff00ebd86ecd8b78c)
(cherry picked from commit 19ec0a5536204105be78744b436a35710d8e8702)
(cherry picked from commit c3717ae4deb8acb43f861675dc44f689def544ed)
(cherry picked from commit 6c74bbe5757b290c2fe5ea13cd980a2b11fb207e)
(cherry picked from commit 9cb48db780c3592a6aa1df2770a309729eca35f6)
(cherry picked from commit 19cb774553302a7ece9d653d052b6de4c47de687)
(cherry picked from commit ac35eb83cd6f34da6079ec4ba8d00390aa56a0c0)
(cherry picked from commit 986a306d221b14891d1e5776ad3088d5636595cb)

.gitattributes

@@ -1,5 +1,5 @@
 * text=auto eol=lf
-*.tmpl linguist-language=Handlebars
+*.tmpl linguist-language=go-html-template
 /assets/*.json linguist-generated
 /public/assets/img/svg/*.svg linguist-generated
 /templates/swagger/v1_json.tmpl linguist-generated