Don't run release.yml on push except in testing

For now, this makes it so the `workflow_dispatch` event has to be
used to run the `release.yml` workflow, except for fake testing
releases (tags that end in `-DO-NOT-USE`).

As noted in the explanatory comment, the `push` event rarely if
ever occurs when tags are pushed to the `GitoxideLabs/gitoxide`
repository. It is uncommon for a `gitoxide` crate release to be
tagged at a commit that does not also have three or more library
crates tagged. But `cargo smart-release` pushes all relevant tags
at once, and GitHub Actions currently does not register a `push`
event when more than three tags are pushed together. So the
`release.yml` workflow is run via `workflow_dispatch` instead.

The preceding commit adds `justfile` recipes to make it easier to
trigger `release.yml` via `workflow_dispatch`. But this runs the
risk that, in the rare case that there are few enough tags pushed
for the `push` trigger to work, the workflow might be run more than
once for the same release. Therefore, this prevents `push` from
ever triggering the workflow for tags representing actual releases.

See GitoxideLabs#1970 for some other details.

(Allowing `push` to still work in testing makes it easier to test
in a fork without risking accidentally triggering the workflow in
the upstream repository. So the pattern is narrowed to still allow
that, rather than being removed altogether, at least for now.)

Author: EliahKagan

.github/workflows/release.yml

@@ -7,9 +7,16 @@ on:
   push:
     # Enable when testing release infrastructure on a branch.
     # branches:
-     #  - fix-releases
+    #   - fix-releases
     tags:
-      - 'v*'
+    # For now, real releases always use `workflow_dispatch`, and running the workflow on tag pushes
+    # is only done in testing. This is because we usually push too many tags at once for the `push`
+    # event to be triggered, since there are usually more than 3 crates tagged together. So the
+    # `push` trigger doesn't usually work. If we allow it, we risk running the workflow twice if
+    # it is also manually triggered based on the assumption that it would not run. See #1970 for
+    # details. See also the `run-release-workflow` and `roll-release` recipes in the `justfile`.
+    # - 'v*'
+      - 'v*-DO-NOT-USE'  # Pattern for tags used to test the workflow (usually done in a fork).
   workflow_dispatch:
 
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