Allow making GitHub Release Pages from main branch commits with tags

Previously, only branches by the pattern `releases/*`
were able to start "Make Release" workflow on GitHub Actions.

By this patch, the branch `main` is the only branch capable of
using "Make Release" workflow. Git tag must be set, otherwise
the builds will be kept as GitHub Actions Artifacts only, without
making GitHub Release Page.

.github/workflows/build.yml

@@ -1,26 +1,19 @@
 #
-# Anything pushed into the branch `releases/*` with a tag will be published
+# Anything pushed into the branch `main` with a tag will be published
 # on GitHub Release Page as draft upon succesful build and test on three
 # operating systems and Python >= 3.8.
 #
-# Recommended branch names for releases: `releases/5.x`, `releases/6.x`.
 # Git tag specifies exact version. Example of git tags: `v5.0.0`,
 # `v6.0.0`, `v6.5.1`.
 #
 # Anything pushed into a different branch will be built and tested without
 # making any release on GitHub Release Page.
 #
 # Pull Requests will be built and tested without making any release on GitHub
-# Release Page. Merge the branch 'releases/*' with the Pull Request and get
-# a new GitHub Release (draft), if git tag is set.
+# Release Page. Merge the branch 'main' with the Pull Request and get
+# a new GitHub Release (draft) ONLY if a git tag is set.
 #
-# Normally, validated Pull Requests are going into `main` branch.
-# Once it is considered that the release can be made, just place
-# any commits from `main` into `releases/*` (e.g. `releases/6.x`) and
-# set appropriate tag, e.g. `v6.0.7`, then push the releases branch to GitHub.
-# This way GitHub Release Page creation can be automated.
-#
-# If you pushed the release branch to GitHub and forgot to set tag name,
+# If you updated the main branch on GitHub and forgot to set a tag name,
 # the release won't published (as draft) on GitHub Release Page. No worries,
 # add the tag later and restart the workflow in GitHub Actions for the
 # commit which already was in the workflow.
@@ -592,7 +585,7 @@ jobs:
       - build-macos-py38
     name: Make Release
     runs-on: ubuntu-22.04
-    if: ${{ startsWith(needs.prepare-build-info.outputs.tagname, 'v') && startsWith(needs.prepare-build-info.outputs.branchname, 'releases/') }}
+    if: ${{ startsWith(needs.prepare-build-info.outputs.tagname, 'v') && needs.prepare-build-info.outputs.branchname == 'main' }}
     permissions:
       # IMPORTANT: mandatory for GitHub Releases
       contents: write