Replace egrep with grep -E in Makefile (#3362)

egrep is deprecated and warns about this since version 3.8:
https://www.gnu.org/software/grep/manual/grep.html

Makefile

@@ -17,7 +17,7 @@ TOOLS_MOD_DIR := ./internal/tools
 ALL_DOCS := $(shell find . -name '*.md' -type f | sort)
 ALL_GO_MOD_DIRS := $(shell find . -type f -name 'go.mod' -exec dirname {} \; | sort)
 OTEL_GO_MOD_DIRS := $(filter-out $(TOOLS_MOD_DIR), $(ALL_GO_MOD_DIRS))
-ALL_COVERAGE_MOD_DIRS := $(shell find . -type f -name 'go.mod' -exec dirname {} \; | egrep -v '^./example|^$(TOOLS_MOD_DIR)' | sort)
+ALL_COVERAGE_MOD_DIRS := $(shell find . -type f -name 'go.mod' -exec dirname {} \; | grep -E -v '^./example|^$(TOOLS_MOD_DIR)' | sort)
 
 GO = go
 TIMEOUT = 60