Adjust to newer CLI behavior (#678)

When no dependencies are found or need to be updated, the CLI no longer
creates an empty buf.lock file. Update the fetch script to gracefully
handle this.

Fixes #676.

Makefile

@@ -7,7 +7,7 @@ MAKEFLAGS += --warn-undefined-variables
 MAKEFLAGS += --no-builtin-rules
 MAKEFLAGS += --no-print-directory
 BIN := .tmp/bin
-BUF_VERSION ?= v1.34.0
+BUF_VERSION ?= v1.38.0
 COPYRIGHT_YEARS := 2021-2023
 GOLANGCI_LINT_VERSION ?= v1.58.0
 LICENSE_IGNORE := --ignore /testdata/

scripts/fetch.sh

@@ -65,9 +65,9 @@ process_ref() {
   # file since it's no longer relevant: each BSR cluster will sync itself from the base files and
   # regenerate its own `buf.lock`.
   pushd "${mod_tmp_path}" > /dev/null
-  buf mod update
+  buf dep update
   buf build
-  rm buf.lock
+  rm -f buf.lock
   popd > /dev/null
 
   # process the prepared module: convert it to CAS from the tmp mod directory and put blob files in