ci: run Forgejo Actions & Packages test w/ dynamic matrix (#1367)

Incorporates these changes:
- When `forgejo/build-from-sources` is present, Actions & Packages tests are run only against the built versions.  Otherwise, they are run against the versions defined in `$RELEASE_NUMBERS`
- Updates Packages tests which are testing Alpine publishing to use currently supported Alpine releases
- Actions & Packages tests are run in a matrix, allowing parallel execution

Only the Actions & Packages tests take a significant amount of time (>10 minutes), so changes have been limited to those test suites -- every test suite that is moved into a matrix adds additional overhead in the 1 minute `prepare-end-to-end` step.

Reviewed-on: https://code.forgejo.org/forgejo/end-to-end/pulls/1367
Co-authored-by: Mathieu Fenniak <mathieu@fenniak.net>
Co-committed-by: Mathieu Fenniak <mathieu@fenniak.net>

packages/packages.sh

@@ -7,5 +7,7 @@ PACKAGES_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 source $PACKAGES_DIR/alpine.sh
 
 function test_packages() {
-    run test_packages_alpine
+    local forgejo_versions="${1:-$RELEASE_NUMBERS}"
+
+    run test_packages_alpine $forgejo_versions
 }