Add skip_fetch input option

This new option will allow users to skip the execution of `git fetch` if it has a negative impact in their workflows.

In a future PR I will probably remove the call to git-fetch interely. It was added in #108 in relation to a problem with slashes in branch names. That problem wasn't properly fixed though.

entrypoint.sh

@@ -41,7 +41,12 @@ _switch_to_branch() {
     echo "INPUT_BRANCH value: $INPUT_BRANCH";
 
     # Fetch remote to make sure that repo can be switched to the right branch.
-    git fetch --depth=3;
+
+    if "$INPUT_SKIP_FETCH"; then
+        echo "::debug::git-fetch has not been executed";
+    else
+        git fetch --depth=3;
+    fi
 
     # Switch to branch from current Workflow run
     # shellcheck disable=SC2086