Workaround for GitHub Actions

https://github.com/sue445/go-gem-wrapper/actions/runs/10475042353/job/29010778469?pr=108

```
+ rake go:test
CGO_CFLAGS=-O3 -fno-fast-math -ggdb3 -Wall -Wextra -Wdeprecated-declarations -Wdiv-by-zero -Wduplicated-cond -Wimplicit-function-declaration -Wimplicit-int -Wpointer-arith -Wwrite-strings -Wold-style-definition -Wimplicit-fallthrough=0 -Wmissing-noreturn -Wno-cast-function-type -Wno-constant-logical-operand -Wno-long-long -Wno-missing-field-initializers -Wno-overlength-strings -Wno-packed-bitfield-compat -Wno-parentheses-equality -Wno-self-assign -Wno-tautological-compare -Wno-unused-parameter -Wno-unused-value -Wsuggest-attribute=format -Wsuggest-attribute=noreturn -Wunused-variable -Wmisleading-indentation -Wundef  -fPIC -I/opt/hostedtoolcache/Ruby/3.3.4/x64/include/ruby-3.3.0/x86_64-linux -I/opt/hostedtoolcache/Ruby/3.3.4/x64/include/ruby-3.3.0 CGO_LDFLAGS=-L/opt/hostedtoolcache/Ruby/3.3.4/x64/lib -lruby -Wl,--unresolved-symbols=ignore-all go test -count=1 ${TEST_ARGS}
go: downloading github.com/stretchr/testify v1.9.0
go: downloading github.com/davecgh/go-spew v1.1.1
go: downloading github.com/pmezard/go-difflib v1.0.0
go: downloading gopkg.in/yaml.v3 v3.0.1
gcc_fatalf.c: In function ‘fatalf’:
gcc_fatalf.c:19:9: error: function ‘fatalf’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
   19 |         vfprintf(stderr, format, ap);
      |         ^~~~~~~~
gcc_fatalf.c: At top level:
cc1: note: unrecognized command-line option ‘-Wno-self-assign’ may have been intended to silence earlier diagnostics
cc1: note: unrecognized command-line option ‘-Wno-parentheses-equality’ may have been intended to silence earlier diagnostics
cc1: note: unrecognized command-line option ‘-Wno-constant-logical-operand’ may have been intended to silence earlier diagnostics
cc1: all warnings being treated as errors
```

Author: sue445

Rakefile

@@ -22,6 +22,16 @@ def env_vars
 
   cflags = "#{RbConfig::CONFIG["CFLAGS"]} -I#{RbConfig::CONFIG["rubyarchhdrdir"]} -I#{RbConfig::CONFIG["rubyhdrdir"]}"
 
+  # FIXME: Workaround for GitHub Actions
+  if ENV["GITHUB_ACTIONS"]
+    cflags.gsub!("-Wno-self-assign", "")
+    cflags.gsub!("-Wno-parentheses-equality", "")
+    cflags.gsub!("-Wno-constant-logical-operand", "")
+    cflags.gsub!("-Wsuggest-attribute=format", "")
+    cflags.gsub!("-Wold-style-definition", "")
+    ldflags.gsub!("-Wl,--unresolved-symbols=ignore-all", "")
+  end
+
   {
     "CGO_CFLAGS" => cflags,
     "CGO_LDFLAGS" => ldflags,