CONTRIBUTING.md: change table column order for staging

The graph right above the table has the order as `master` ⇒ `staging-next` ⇒ `staging`.
This corresponds with the workflow, i.e. automatic merges happen in that direction and the manual merging is in reverse direction of that.
As a first time reader of this document the table was very confusing due to the disparity of that.
With this change the table should read more fluently for people not familiar with the workflow since the table follows the step-by-step flow of commits.

Signed-off-by: benaryorg <binary@benary.org>

CONTRIBUTING.md

@@ -439,14 +439,14 @@ gitGraph
 
 Here's an overview of the different branches:
 
-| branch | `master` | `staging` | `staging-next` |
+| branch | `master` | `staging-next` | `staging` |
 | --- | --- | --- | --- |
-| Used for development | ✔️ | ✔️ | ❌ |
-| Built by Hydra | ✔️ | ❌ | ✔️ |
-| [Mass rebuilds][mass-rebuild] | ❌ | ✔️ | ⚠️  Only to fix Hydra builds |
-| Critical security fixes | ✔️ for non-mass-rebuilds | ❌ | ✔️ for mass-rebuilds |
-| Automatically merged into | `staging-next` | - | `staging` |
-| Manually merged into | - | `staging-next` | `master` |
+| Used for development | ✔️ | ❌ | ✔️ |
+| Built by Hydra | ✔️ | ✔️ | ❌ |
+| [Mass rebuilds][mass-rebuild] | ❌ | ⚠️  Only to fix Hydra builds | ✔️ |
+| Critical security fixes | ✔️ for non-mass-rebuilds | ✔️ for mass-rebuilds | ❌ |
+| Automatically merged into | `staging-next` | `staging` | - |
+| Manually merged into | - | `master` | `staging-next` |
 
 The staging workflow is used for all main branches, `master` and `release-YY.MM`, with corresponding names:
 - `master`/`release-YY.MM`