chore: upgrade alexflint/go-arg (#375)

Upgrade version of alexflint/go-arg from 1.4.2 to 1.5.1 to avoid an
issue installing `genqlcient`:

```
./../../go/pkg/mod/github.com/alexflint/[email protected]/parse.go:13:2: github.com/alexflint/[email protected]: verifying module: checksum mismatch
```


I have:
- [x] Written a clear PR title and description (above)
- [x] Signed the [Khan Academy CLA](https://www.khanacademy.org/r/cla)
- [x] Added tests covering my changes, if applicable
- [x] Included a link to the issue fixed, if applicable
- [x] Included documentation, for new features
- [x] Added an entry to the changelog

---------

Co-authored-by: Casey Lee <[email protected]>
Co-authored-by: Craig Silverstein <[email protected]>

Author: 3 people

docs/CHANGELOG.md

@@ -27,6 +27,7 @@ When releasing a new version:
 ### Bug fixes:
 
 - fixed documentation link in `introduction.md`
+- upgraded version of alexflint/go-arg from 1.4.2 to 1.5.1
 
 ## v0.8.0
 

go.mod

@@ -6,7 +6,7 @@ toolchain go1.23.3
 
 require (
 	github.com/99designs/gqlgen v0.17.57
-	github.com/alexflint/go-arg v1.4.2
+	github.com/alexflint/go-arg v1.5.1
 	github.com/bmatcuk/doublestar/v4 v4.6.1
 	github.com/bradleyjkemp/cupaloy/v2 v2.6.0
 	github.com/google/uuid v1.6.0
@@ -19,7 +19,7 @@ require (
 
 require (
 	github.com/agnivade/levenshtein v1.1.1 // indirect
-	github.com/alexflint/go-scalar v1.0.0 // indirect
+	github.com/alexflint/go-scalar v1.2.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
 	github.com/hashicorp/golang-lru/v2 v2.0.7 // indirect