Fix: egrep is obsolescent, use grep -E

See e.g., egrep(1) [https://linux.die.net/man/1/egrep]:

> two variant programs egrep and fgrep are available. egrep is the same
> as grep -E. fgrep is the same as grep -F. Direct invocation as either
> egrep or fgrep is deprecated

See also the rationale of the POSIX description of grep
(https://pubs.opengroup.org/onlinepubs/9699919799/utilities/grep.html):

> This grep has been enhanced in an upwards-compatible way to provide
> the exact functionality of the historical egrep and fgrep commands as
> well. It was the clear intention of the standard developers to
> consolidate the three greps into a single command.

Closes: #839

docker/Dockerfile.build.ubuntu22.cross-arm64

@@ -48,7 +48,7 @@ RUN /bin/sh oaienv && \
     # making always passing so we can analyze the all.txt file
     ninja dlsim ulsim ldpctest polartest smallblocktest nr_pbchsim nr_dlschsim nr_ulschsim nr_dlsim nr_ulsim nr_pucchsim nr_prachsim lte-softmodem nr-softmodem nr-cuup oairu lte-uesoftmodem nr-uesoftmodem params_libconfig coding rfsimulator > ../../log/all.txt 2>&1; \
     # displaying errors and warnings
-    egrep -A3 "warning:|error:" ../../log/all.txt || true && \
+    grep -E -A3 "warning:|error:" ../../log/all.txt || true && \
     # will fail only if string "errors:" is found
-    egrep "error:" -vqz ../../log/all.txt && \
+    grep -E "error:" -vqz ../../log/all.txt && \
     echo "====== End of log for cross-build executables ======"