[CrashReporting] Enable http_retry, harden symbol upload, fix NSIS context

Sets sentry_options_set_http_retry so the cache_keep-held crash
envelope in Ask mode is written with a retry filename and actually
flushes on giveConsent() instead of sitting in <db>/cache until
pruning.

Adds continue-on-error to both sentry-cli install steps so a Sentry
registry outage or broken Git Bash install cannot block release
assets.

Cleans the legacy WER CrashDumps folder under SetShellVarContext
current (under all it resolves to ProgramData, not the user's
AppData) in installer and uninstaller; registry delete works in
either context.

.github/workflows/desktop-build.yml

@@ -270,6 +270,9 @@ jobs:
 
       - name: "Install sentry-cli"
         if: matrix.package != 'skip' && needs.configure.outputs.tag != null
+        # Downloads from Sentry's release registry: a Sentry outage or a broken install under
+        # Git Bash must not take down the release assets below.
+        continue-on-error: true
         shell: bash
         env:
           SENTRY_CLI_VERSION: '3.8.0'
@@ -621,6 +624,9 @@ jobs:
 
       - name: "Install sentry-cli"
         if: needs.configure.outputs.tag != null && matrix.make_package == '1'
+        # Same as the Linux leg above: the install downloads from Sentry's registry, so a
+        # failure here must not block the release upload below.
+        continue-on-error: true
         shell: bash
         env:
           SENTRY_CLI_VERSION: '3.8.0'