fix: cleaner mastodon post (#435)

part of an effort to harmonize Mastodon posts in the Snakemake ecosystem

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Chores**
* Updated release announcement image and messaging for social media
posts.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: cmeesters

.github/workflows/announce-release.yml

@@ -32,7 +32,7 @@ jobs:
         with:
           access-token: ${{ secrets.MASTODONBOT }}
           pr-title: ${{ github.event.head_commit.message }}
-          image: "long_logo_hpc.png"
+          image: "logo_dark.png"
           image-description: "Snakemake HPC logo for Mastodon"
           repotitle: "Snakemake Executor Plugin for SLURM"
           message: |
@@ -42,9 +42,9 @@ jobs:
             
             Give us some time, and you will automatically find the plugin on #Bioconda and #Pypi.
             
-            This plugin is relevant for #HPC users using the #SLURM batch system. If you want to 
-            discuss the release, you will find the maintainers here on Mastodon!
-            @rupdecat and @johanneskoester@fosstodon.org
+            This plugin is relevant for #HPC users using the #SLURM batch system. 
+            The maintainers are here on Mastodon -
+            @rupdecat and @johanneskoester@fosstodon.org.
             
             If you discover any issues, please report them on {{ issue_url }}.