[chore][scoped-test] Don't do a literal expansion for changed files (open-telemetry#37298)

Doing in place expansion leads to hitting bash line size limits, this is
a cheap improvement that makes less likely to hit cases like open-telemetry#37287.

Tests on my fork
https://github.com/pjanotti/opentelemetry-service-contrib/actions/runs/12836050460/job/35796880868

Author: pjanotti

Makefile.Common

@@ -268,11 +268,11 @@ CHANGED_GOLANG_SOURCES?=$(shell git diff main --name-only | grep -E '.*\.go$$' |
 .PHONY: for-affected-components
 for-affected-components:
 	@echo "Checking for affected components..."
-	@if [ -z '$(CHANGED_GOLANG_SOURCES)' ]; then \
+	@if [ -z '$${CHANGED_GOLANG_SOURCES}' ]; then \
 		echo "No go source changes detected in shippable code."; \
 	else \
 		cd $(SRC_ROOT); \
-		DEPENDENT_PKGS=$$(echo $(CHANGED_GOLANG_SOURCES) | xargs sed -n 's|^package .* // import "\(.*\)"$$|\1|p' | uniq); \
+		DEPENDENT_PKGS=$$(echo $${CHANGED_GOLANG_SOURCES} | xargs sed -n 's|^package .* // import "\(.*\)"$$|\1|p' | uniq); \
 		if [ -z '$${DEPENDENT_PKGS}' ]; then \
 			echo "No other package depends on the one being changed."; \
 		else \
@@ -289,11 +289,11 @@ CHANGED_GOLANG_TESTS?=$(shell git diff main --name-only | grep -E '.*_test\.go$$
 .PHONY: run-changed-tests
 run-changed-tests:
 	@echo "Checking for affected tests..."
-	@if [ -z '$(CHANGED_GOLANG_TESTS)' ]; then \
+	@if [ -z '$${CHANGED_GOLANG_TESTS}' ]; then \
 		echo "No go test changes detected."; \
 	else \
 		cd $(SRC_ROOT); \
-		AFFECTED_TEST_DIRS=$$(echo $(CHANGED_GOLANG_TESTS) | tr ' ' '\n' | xargs dirname | uniq); \
+		AFFECTED_TEST_DIRS=$$(echo $${CHANGED_GOLANG_TESTS} | tr ' ' '\n' | xargs dirname | uniq); \
 		if [ -z '$${AFFECTED_TEST_DIRS}' ]; then \
 			echo "Failed to find the affected test directories."; \
 		else \