build: bump version number to 13.8.0 #2666

Job	Run time
build (ubuntu-latest)	3m 32s
java_matrix	2s
build (macos-latest)	3m 37s
download_test_data	6s
unit_tests (21)	3m 38s
unit_tests (25)	4m 16s
test_run-groovy	37s
test_decoder	2m 5s
test_coatjava (ubuntu-latest, eb-epc)	2m 26s
test_coatjava (macos-latest, eb-ep, ./run-eb-tests.sh -100 electronproton)	3m 35s
test_clara	4m 34s
spotbugs	6m 51s
test_coatjava (ubuntu-latest, kpp)	3m 32s
test_coatjava (ubuntu-latest, eb-eftpi)	3m 0s
test_coatjava (ubuntu-latest, eb-ep)	2m 55s
test_coatjava (ubuntu-latest, eb-enc)	2m 17s
test_coatjava (ubuntu-latest, eb-eg)	2m 23s
release_build	-1s
generate_documentation	1m 2s
deploy_web_pages	0s
final	2s
	50m 29s

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