debian: disable salsa CI on non-debian branches

The Salsa CI attempts to do a package build, and the debian/patches
directory is generally not set up correctly for a successful source
build on non-debian branches.  So skip them to avoid failed builds and
to avoid wasting CI bandwidth.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

debian/salsa-ci.yml

@@ -1,3 +1,7 @@
 include:
   - https://salsa.debian.org/salsa-ci-team/pipeline/raw/master/salsa-ci.yml
   - https://salsa.debian.org/salsa-ci-team/pipeline/raw/master/pipeline-jobs.yml
+  - https://salsa.debian.org/salsa-ci-team/pipeline/raw/master/recipes/debian.yml
+
+variables:
+  SALSA_CI_IGNORED_BRANCHES: 'web|next|master|maint|old-maint|pristine-tar|pu'