ci: use portable shell commands

Author: orien

.woodpecker/release.yaml

@@ -33,7 +33,6 @@ steps:
   validate-tag:
     image: alpine:latest
     commands:
-      - apk add --no-cache bash
       - |
         TAG="${CI_COMMIT_TAG}"
         echo "Release tag: $TAG"
@@ -51,11 +50,10 @@ steps:
     image: alpine:latest
     depends_on: [validate-tag]
     commands:
-      - apk add --no-cache bash
       - |
         TAG="${CI_COMMIT_TAG}"
         VERSION_FROM_FILE=$(cat VERSION)
-        VERSION_FROM_TAG="${TAG#v}"
+        VERSION_FROM_TAG="$(echo "$TAG" | sed 's/^v//')"
 
         echo "Tag version: $VERSION_FROM_TAG"
         echo "VERSION file: $VERSION_FROM_FILE"