CI: Expect 4 test plugins to pass the validate action

The discrete_params test plugin is now built alongside the other test
plugins, so the validate action's glob finds four of them. It passes at
the action's default strictness level of 5.

Author: drowaudio

.github/workflows/acceptance.yml

@@ -156,7 +156,7 @@ jobs:
         shell: bash
         run: |
           check() { echo "$1: got '$2', expected '$3'"; [ "$2" = "$3" ] || exit 1; }
-          check "validate passed"            "${{ steps.validate.outputs.passed }}"           3
+          check "validate passed"            "${{ steps.validate.outputs.passed }}"           4
           check "validate failed"            "${{ steps.validate.outputs.failed }}"           0
           check "validate-missing outcome"   "${{ steps.validate-missing.outcome }}"          failure
           check "validate-missing passed"    "${{ steps.validate-missing.outputs.passed }}"   1