3.11.0: system browser sign-in, update check limited to 3.x, GitHub templates

.github/pull_request_template.md

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+<!--
+  Target branch
+
+    Fixing version 3?  target  Development
+    Fixing version 4?  target  v4
+
+  A pull request opened against the default branch is retargeted to
+  Development before review. Use the Edit button next to the title.
+-->
+
+<!--
+  How version 4 changes are applied during the beta
+
+  Version 4 is developed elsewhere and the v4 branch is published as one
+  snapshot per release, not as a running history. An accepted change is
+  applied upstream and appears in the next release, so your commit will not
+  show up in this branch. You are credited in the release notes instead.
+  Nothing is lost, and nothing needs doing on your side.
+-->
+
+## What does this change?
+
+<!-- One or two sentences. What was wrong, or what is now possible. -->
+
+## Related issue
+
+<!-- "Fixes #123", or "none" if there isn't one. -->
+
+## How was it tested?
+
+<!--
+  Which version, which cloud, and which operating system, since 4.0 runs on
+  three. If it touches sign-in, say which method you used: embedded window,
+  Web Account Manager, system browser, device code, or an application identity.
+-->
+
+- Version:
+- Cloud:
+- Operating system and PowerShell version:
+- Tests run:
+
+## Anything a reviewer should know
+
+<!--
+  Behaviour that changes for existing users, a setting that moves, a file format
+  that shifts. Say so here rather than leaving it to be discovered.
+-->