Fix mockbuild user missing in chroot

The AlmaLinux 10 mock base config does not create the mockbuild user
inside the chroot, causing 'Failed to resolve user mockbuild' during
SRPM installation. Add explicit user creation via mock --chroot
after --init, and use --scrub=all + --no-clean to prevent stale
state from interfering.

.forgejo/workflows/build-rpms.yml

@@ -50,7 +50,7 @@ jobs:
 
       - name: Build RPM with mock
         run: |
-          cat > /tmp/mock-custom.cfg <<'MOCKEOF'
+          cat > /etc/mock/custom.cfg <<'MOCKEOF'
           include('/etc/mock/alma+epel-10-x86_64.cfg')
           config_opts['root'] = 'custom'
           config_opts['yum.conf'] += """
@@ -71,13 +71,11 @@ jobs:
           enabled=1
           """
           MOCKEOF
-          cp /tmp/mock-custom.cfg /etc/mock/custom.cfg
-          mock --root custom --scrub=chroot || true
-          mock \
-            --root custom \
-            --resultdir "${HOME}/mock-results" \
-            --clean \
-            --rebuild "${{ env.SRPM_PATH }}"
+
+          mock --root custom --scrub=all || true
+          mock --root custom --init
+          mock --root custom --chroot 'groupadd -g 135 mock 2>/dev/null || true; useradd -u 135 -g 135 -d /builddir -s /bin/bash mockbuild 2>/dev/null || true'
+          mock --root custom --resultdir "${HOME}/mock-results" --no-clean --rebuild "${{ env.SRPM_PATH }}"
 
       - name: Upload RPMs to Forgejo Package Registry
         run: |