build(deps): Bump go.opentelemetry.io/collector/cmd/mdatagen

Bumps [go.opentelemetry.io/collector/cmd/mdatagen](https://github.com/open-telemetry/opentelemetry-collector) from 0.20.0 to 0.21.0.
- [Release notes](https://github.com/open-telemetry/opentelemetry-collector/releases)
- [Changelog](https://github.com/open-telemetry/opentelemetry-collector/blob/main/CHANGELOG.md)
- [Commits](open-telemetry/opentelemetry-collector@v0.20.0...v0.21.0)

Signed-off-by: dependabot[bot] <support@github.com>

internal/tools/go.mod

@@ -10,5 +10,5 @@ require (
 	github.com/pavius/impi v0.0.3
 	github.com/tcnksm/ghr v0.13.0
 	go.opentelemetry.io/collector/cmd/issuegenerator v0.21.0
-	go.opentelemetry.io/collector/cmd/mdatagen v0.20.0
+	go.opentelemetry.io/collector/cmd/mdatagen v0.21.0
 )

internal/tools/go.sum

@@ -530,8 +530,8 @@ go.opencensus.io v0.22.3/go.mod h1:yxeiOL68Rb0Xd1ddK5vPZ/oVn4vY4Ynel7k9FzqtOIw=
 go.opencensus.io v0.22.4/go.mod h1:yxeiOL68Rb0Xd1ddK5vPZ/oVn4vY4Ynel7k9FzqtOIw=
 go.opentelemetry.io/collector/cmd/issuegenerator v0.21.0 h1:O13DYk7fRa9+dJe1ZhdyERY09abBPf3EQXCEEt2RPLI=
 go.opentelemetry.io/collector/cmd/issuegenerator v0.21.0/go.mod h1:XHD/HQbAwVt/9xOUVnT8ZffHO9Rj5a8Z2WVwwTNRlQ8=
-go.opentelemetry.io/collector/cmd/mdatagen v0.20.0 h1:xxCYRdc2JybPBO13x5jZ5JxUbAxPAk0y4E3UBVAllyI=
-go.opentelemetry.io/collector/cmd/mdatagen v0.20.0/go.mod h1:oWCxEeYMK/9i6cQEVs5YCWr5Q5KZn9uxnLLQxm8j/S4=
+go.opentelemetry.io/collector/cmd/mdatagen v0.21.0 h1:bICODUrEC74scfqNv6f23Z1XnHC3uW7YWPIGTqkO9+w=
+go.opentelemetry.io/collector/cmd/mdatagen v0.21.0/go.mod h1:oWCxEeYMK/9i6cQEVs5YCWr5Q5KZn9uxnLLQxm8j/S4=
 go.uber.org/atomic v1.4.0/go.mod h1:gD2HeocX3+yG+ygLZcrzQJaqmWj9AIm7n08wl/qW/PE=
 go.uber.org/atomic v1.6.0 h1:Ezj3JGmsOnG1MoRWQkPBsKLe9DwWD9QeXzTRzzldNVk=
 go.uber.org/atomic v1.6.0/go.mod h1:sABNBOSYdrvTF6hTgEIbc7YasKWGhgEQZyfxyTvoXHQ=