ci: pin gh action to v2_k7_1_6_3 to resolve build errors

Fixed a build error by specifying the version of a GitHub Action to v2_k7_1_6_3. This addresses an issue where the command `git worktree add --detach --force /tmp/tmpy_4q2jth main` failed. The error was resolved by using v2_k7_1_6_3 until the changes in commit INTI-CMNB/KiBot@d661880 are included in the LTS tag v2_k7. Following the resolution of issue INTI-CMNB/KiBot#589, it will then be necessary to change `main` to `origin/main` in `diff.kibot.yaml`.

.github/workflows/kibot_diff.yml

@@ -15,7 +15,7 @@ jobs:
           fetch-depth: '0'
 
       - name: Run KiBot
-        uses: INTI-CMNB/KiBot@v2_k7
+        uses: INTI-CMNB/KiBot@v2_k7_1_6_3
         with:
           config: kicad/diff.kibot.yaml
           # optional - prefix to output defined in config