[buildbot] ci: centralize BUILDBOT_VERSION in a shared file

[LEDE Commits]

ynezz pushed a commit to buildbot.git, branch main:
https://git.openwrt.org/b15537c62b8d951181e88fb867f1167d0525424a

commit b15537c62b8d951181e88fb867f1167d0525424a
Author: Petr Štetiar <ynezz at true.cz>
AuthorDate: Sun Jan 11 10:34:21 2026 +0100

    ci: centralize BUILDBOT_VERSION in a shared file
    
    Move the buildbot version from duplicate workflow env blocks to a single
    .github/buildbot-version file.
    
    Signed-off-by: Petr Štetiar <ynezz at true.cz>
---
 .github/buildbot-version                    | 1 +
 .github/workflows/build-push.yml            | 3 ++-
 .github/workflows/cleanup-pr-containers.yml | 9 ++++++---
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/.github/buildbot-version b/.github/buildbot-version
new file mode 100644
index 0000000..b6d8b76
--- /dev/null
+++ b/.github/buildbot-version
@@ -0,0 +1 @@
+3.11.8
diff --git a/.github/workflows/build-push.yml b/.github/workflows/build-push.yml
index 31f3920..84004b9 100644
--- a/.github/workflows/build-push.yml
+++ b/.github/workflows/build-push.yml
@@ -14,7 +14,6 @@ on:
         type: number
 
 env:
-  BUILDBOT_VERSION: 3.11.8
   GITHUB_SHA_LEN: 8
 
 concurrency:
@@ -77,6 +76,7 @@ jobs:
 
       - name: Environment variables
         run: |
+          echo "BUILDBOT_VERSION=$(cat .github/buildbot-version)" >> $GITHUB_ENV
           echo "GIT_SHA_SHORT=${GITHUB_SHA::${{ env.GITHUB_SHA_LEN }}}" >> $GITHUB_ENV
 
       - name: Build container and export it to local Docker
@@ -121,6 +121,7 @@ jobs:
 
       - name: Environment variables
         run: |
+          echo "BUILDBOT_VERSION=$(cat .github/buildbot-version)" >> $GITHUB_ENV
           echo "GIT_SHA_SHORT=${GITHUB_SHA::${{ env.GITHUB_SHA_LEN }}}" >> $GITHUB_ENV
 
       - name: Docker meta
diff --git a/.github/workflows/cleanup-pr-containers.yml b/.github/workflows/cleanup-pr-containers.yml
index 073b4b8..ddef073 100644
--- a/.github/workflows/cleanup-pr-containers.yml
+++ b/.github/workflows/cleanup-pr-containers.yml
@@ -4,9 +4,6 @@ on:
   pull_request:
     types: [closed]
 
-env:
-  BUILDBOT_VERSION: 3.11.8
-
 jobs:
   cleanup:
     name: Delete PR container images
@@ -21,6 +18,12 @@ jobs:
           - worker
 
     steps:
+      - name: Checkout
+        uses: actions/checkout at v5
+
+      - name: Read Buildbot version
+        run: echo "BUILDBOT_VERSION=$(cat .github/buildbot-version)" >> $GITHUB_ENV
+
       - name: Delete PR container image
         uses: actions/delete-package-versions at v5
         with: