Remove tj-actions/branch-names from build workflow

Replace tj-actions/branch-names with github.ref_name which provides
the branch name natively without a third-party action. The tj-actions
GitHub namespace was compromised in March 2025 (CVE-2025-30066) and
using actions from that namespace is no longer recommended. Pass the
value via env: to avoid shell interpolation of untrusted input in
run: blocks.

Jira: OSPRH-31730

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Martin Schuppert <mschuppert@redhat.com>

Author: stuggi

.github/workflows/edpm-bootc.yaml

@@ -42,14 +42,12 @@ jobs:
     steps:
     - uses: actions/checkout@v4
 
-    - name: Get branch name
-      id: branch-name
-      uses: tj-actions/branch-names@v8
-
     - name: Set latest tag for non main branch
-      if: "${{ steps.branch-name.outputs.current_branch != 'main' }}"
+      if: github.ref_name != 'main'
+      env:
+        BRANCH_NAME: ${{ github.ref_name }}
       run: |
-        echo "latesttag=${{ steps.branch-name.outputs.current_branch }}-latest" >> $GITHUB_ENV
+        echo "latesttag=${BRANCH_NAME}-latest" >> $GITHUB_ENV
 
     - name: Set EDPM_* env vars
       run: |