ci: handle presence/absence of "static" and "static-charm" envs (#1590)

The observability charms we test against now have a mixture of
environment names, so check whether each is present before trying to run
them.

.github/workflows/observability-charm-tests.yaml

@@ -48,6 +48,43 @@ jobs:
         if: ${{ !(matrix.disabled) }}
         run: tox -vve unit
 
+      - name: Check if 'scenario' tox environment exists
+        id: check-tox-env-scenario
+        run: |
+          if tox --listenvs | grep -q "^scenario$"; then
+            echo "exists=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "exists=false" >> "$GITHUB_OUTPUT"
+          fi
+
+      # alertmanager-k8s has old Scenario tests, so we can't do this until those
+      # are updated.
+#      - name: Run the charm's scenario unit tests
+#        if: ${{ steps.check-tox-env-scenario.outputs.exists == 'true' && !(matrix.disabled) }}
+#        run: tox -vve scenario
+
+      - name: Check if 'static' tox environment exists
+        id: check-tox-env-static
+        run: |
+          if tox --listenvs | grep -q "^static$"; then
+            echo "exists=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "exists=false" >> "$GITHUB_OUTPUT"
+          fi
+
       - name: Run the charm's static analysis checks
-        if: ${{ !(matrix.disabled) }}
+        if: ${{ steps.check-tox-env-static.outputs.exists == 'true' && !(matrix.disabled) }}
+        run: tox -vve static
+
+      - name: Check if 'static-charm' tox environment exists
+        id: check-tox-env-static-charm
+        run: |
+          if tox --listenvs | grep -q "^static-charm$"; then
+            echo "exists=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "exists=false" >> "$GITHUB_OUTPUT"
+          fi
+
+      - name: Run the charm's static (charm) analysis checks
+        if: ${{ steps.check-tox-env-static-charm.outputs.exists == 'true' && !(matrix.disabled) }}
         run: tox -vve static-charm