Add missing git icons (#995)

* Add `git-pull-request-create` icon

* Add `git-pull-request-create-arrow` variant

* Improve `git-*` icons metadata

* Optimise `git-pull-request-closed` icon

* Refine `git-fork` icon

…to match [`network`](https://lucide.dev/icons/network)

* Add `git-graph` icon

* Rename `git-commit` to `git-commit-horizontal`

* Add `git-commit-vertical` icon

* Add `git-pull-request-arrow` icon

* Add `git-compare-arrows` icon

icons/git-pull-request.json

@@ -7,9 +7,11 @@
   ],
   "tags": [
     "code",
-    "version control"
+    "version control",
+    "open"
   ],
   "categories": [
-    "development"
+    "development",
+    "arrows"
   ]
 }