fix(ci): correctly set shell for rename command

It looks like Drone executes all commands with sh, even if the default shell of the container is something else. Because sh does not have support for whitespaces in string extrapolation, the rename command would fail. This change always specifies bash as the shell.

.drone.yml

@@ -1220,7 +1220,7 @@ steps:
     pull: true
     commands:
       - cd desktop/dist
-      - for file in Vikunja*; do suffix=".${file##*.}"; if [[ ! -d $file ]]; then mv "$file" "Vikunja-Desktop-unstable${suffix}"; fi; done
+      - bash -c 'for file in Vikunja*; do suffix=".${file##*.}"; if [[ ! -d $file ]]; then mv "$file" "Vikunja-Desktop-unstable${suffix}"; fi; done'
     depends_on:
       - build
     when:
@@ -1389,6 +1389,6 @@ steps:
         - failure
 ---
 kind: signature
-hmac: 701e3ef16ca217178380a0aacb14601828d9c0d43a7c3cc5033ccd3288927850
+hmac: 2a04bdccf78b768db5ca89bf2bfa472ade15d8499b976b47deb52d93400b38a2
 
 ...