Fix charm build

Newer versions of rpds-py need rust > 1.76; use the right version
from the distro and symlink the versionless binaries.

Add zuul charm build check to validate.

Change-Id: I9f644d97470c6dda679f12a5f4cb18684dd82fec

.zuul.yaml

@@ -2,3 +2,8 @@
     templates:
       - openstack-python3-charm-jobs
       - openstack-cover-jobs
+    check:
+      jobs:
+        - charmbuild
+    vars:
+      charm_build_name: ovn-chassis

charmcraft.yaml

@@ -12,8 +12,14 @@ parts:
     - python3-dev
     - libffi-dev
     - libssl-dev
-    - rustc
+    - rustc-1.76
-    - cargo
+    - cargo-1.76
+    - pkg-config
+    override-build: |
+      # Note(mylesjp): Force build to use rustc-1.76
+      ln -s /usr/bin/rustc-1.76 /usr/bin/rustc
+      ln -s /usr/bin/cargo-1.76 /usr/bin/cargo
+      craftctl default
     build-snaps:
     - charm/latest/edge
     build-environment: