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-closed.json

@@ -7,7 +7,10 @@
   "tags": [
     "code",
     "version control",
-    "rejected"
+    "rejected",
+    "closed",
+    "cancelled",
+    "x"
   ],
   "categories": [
     "development"