fix(pr-validation): install shellcheck via wget instead of apt-get

The act runner container runs as root and apt-get may not be available
or require sudo. Download the pre-built binary tarball directly instead.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/pr-validation.yaml

@@ -34,7 +34,11 @@ jobs:
 
       - name: Install shellcheck
         run: |
-          apt-get update -qq && apt-get install -y -qq shellcheck >/dev/null 2>&1
+          SC_VERSION="v0.10.0"
+          mkdir -p "$HOME/.local/bin"
+          wget -qO- "https://github.com/koalaman/shellcheck/releases/download/${SC_VERSION}/shellcheck-${SC_VERSION}.linux.x86_64.tar.xz" \
+            | tar -xJ --strip-components=1 -C "$HOME/.local/bin" "shellcheck-${SC_VERSION}/shellcheck"
+          echo "$HOME/.local/bin" >> "$GITHUB_PATH"
 
       - name: Shellcheck scripts
         run: |