GitHub Actions: don't execute building ctags executable with -O0 option

https://www.valgrind.org/docs/manual/quick-start.html

    Compile your program with -g to include debugging information so that
    Memcheck's error messages include exact line numbers.  Using -O0 is
    also a good idea, if you can tolerate the slowdown.  With -O1 line
    numbers in error messages can be inaccurate, although generally
    speaking running Memcheck on code compiled at -O1 works fairly well,
    and the speed improvement compared to running -O0 is quite
    significant.  Use of -O2 and above is not recommended as Memcheck
    occasionally reports uninitialised-value errors which don't really
    exist.

Suggested by @leleliu008 at universal-ctags#2747

.github/workflows/testing-with-vlagrind.yml

@@ -7,7 +7,7 @@ on:
     branches: [ master ]
 
 jobs:
-  testing-O0_fixme:
+  testing:
 
     runs-on: ubuntu-latest