Fix typo

Author: Yuki Kobayashi

tox.ini

@@ -57,7 +57,7 @@ setenv =
     coverage75: _DEP_COVERAGE=coverage==7.5.4
     coverage76: _DEP_COVERAGE=coverage==7.6.12
     coverage77: _DEP_COVERAGE=coverage==7.7.1
-    coverage77: _DEP_COVERAGE=coverage==7.8.2
+    coverage78: _DEP_COVERAGE=coverage==7.8.2
     # For testing against a coverage.py working tree.
     coveragedev: _DEP_COVERAGE=-e{env:COVERAGE_HOME}
 passenv =