ci: fire nightly-osp.yml on PR too (temporary, for PR #400 validation)

Add pull_request trigger to nightly-osp.yml so PR #400's reviewers
can see the dispatcher actually fan all 41 reusable workflows out
and the notify job hit Slack.

Marked temporary in the file header -- revert this trigger before
merging if you don't want the full nightly job set firing on every
PR. (For everyday CI, scheduled + workflow_dispatch is the intended
shape.)

Note: PR runs from forks will still hit the private-package issue
for the wolfprov-debs pull (the wolfSSL/wolfProvider repo guard
short-circuits the ORAS step on non-canonical repos). The plumbing
itself -- dispatch, discover-versions, notify, Slack -- runs
regardless and is what this PR-trigger lets you verify end-to-end.

Author: aidangarske

.github/workflows/nightly-osp.yml

@@ -6,14 +6,34 @@ name: Nightly OSP Suite
 # (workflow_call) workflow; this file just fans them out in parallel
 # and reports an aggregate status to Slack.
 #
-# PR CI does NOT run these -- it stays cheap (smoke + simple + a few
-# internal checks). Nightly is where the full matrix lives.
+# Triggers:
+#   - schedule:         daily at 06:00 UTC
+#   - workflow_dispatch: manual fire from the Actions UI
+#   - pull_request:     TEMPORARY -- so PR #400's reviewers can see
+#                       the dispatcher actually fan everything out
+#                       and the notify job hit Slack. Revert this
+#                       trigger before merging if you don't want
+#                       nightly's full job set firing on every PR.
 
 on:
   schedule:
     # 06:00 UTC daily. Pick a time when shared-runner contention is low
     # so the matrix doesn't fight PR CI.
     - cron: '0 6 * * *'
+  pull_request:
+    branches: [ '*' ]
+    types: [opened, synchronize, reopened, ready_for_review]
+    paths-ignore:
+      - '**.md'
+      - 'docs/**'
+      - 'LICENSE*'
+      - '.github/ISSUE_TEMPLATE/**'
+      - '.github/dependabot.yml'
+      - '.gitignore'
+      - 'AUTHORS'
+      - 'COPYING'
+      - 'README*'
+      - 'CHANGELOG*'
   workflow_dispatch:
     inputs:
       reason: