tox.ini quoting seems to have changed too.

Author: Julian

.github/coverage.sh

@@ -0,0 +1,3 @@
+set -e
+printf '### Coverage\n\n' >>$GITHUB_STEP_SUMMARY
+"$1" -m coverage report --format=markdown --show-missing >>$GITHUB_STEP_SUMMARY

tox.ini

@@ -1,4 +1,5 @@
 [tox]
+min_version = 4.0.7
 envlist =
     py{37,38,39,310,311,py3}-{noextra,format,formatnongpl}-{build,tests}
     {noextra,format,formatnongpl}-audit
@@ -15,7 +16,7 @@ passenv = CI, GITHUB_STEP_SUMMARY, PYTHONUTF8
 setenv =
     JSON_SCHEMA_TEST_SUITE = {toxinidir}/json
 
-    coverage,ghcoverage: MAYBE_COVERAGE = coverage run -m
+    coverage,ghcoverage: MAYBE_COVERAGE=coverage run -m
     coverage,ghcoverage: COVERAGE_RCFILE={toxinidir}/.coveragerc
     coverage,ghcoverage: COVERAGE_DEBUG_FILE={envtmpdir}/coverage-debug
     coverage,ghcoverage: COVERAGE_FILE={envtmpdir}/coverage-data
@@ -37,7 +38,7 @@ commands =
 
     coverage: {envpython} -m coverage report --show-missing
     coverage: {envpython} -m coverage html --directory={envtmpdir}/htmlcov
-    ghcoverage: sh -c "printf '### Coverage\n\n' >>$GITHUB_STEP_SUMMARY && {envpython} -m coverage report --format=markdown --show-missing >>$GITHUB_STEP_SUMMARY"
+    ghcoverage: sh {toxinidir}/.github/coverage.sh "{envpython}"
 
     perf: {envpython} {toxinidir}/jsonschema/benchmarks/issue232.py --inherit-environ JSON_SCHEMA_TEST_SUITE {posargs:--output {envtmpdir}/bench-issue232.json}
     perfsuite: {envpython} {toxinidir}/jsonschema/benchmarks/json_schema_test_suite.py --inherit-environ JSON_SCHEMA_TEST_SUITE {posargs:--output {envtmpdir}/bench-json_schema_test_suite.json}