[chore] Use pseudo-version for internal/schemagen (#15282)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

Similar to
#11668 to
fix
https://github.com/open-telemetry/opentelemetry-collector-contrib/actions/runs/25546661845/job/74984423416#step:6:1085

<!-- Issue number if applicable -->
#### Link to tracking issue
Fixes
open-telemetry/opentelemetry-collector-contrib#48219

Signed-off-by: ChrsMark <chrismarkou92@gmail.com>

Author: ChrsMark

cmd/mdatagen/go.mod

@@ -21,7 +21,7 @@ require (
 	go.opentelemetry.io/collector/consumer/xconsumer v0.151.0
 	go.opentelemetry.io/collector/featuregate v1.57.0
 	go.opentelemetry.io/collector/filter v0.151.0
-	go.opentelemetry.io/collector/internal/schemagen v0.0.0
+	go.opentelemetry.io/collector/internal/schemagen v0.0.0-20260508160712-91b32efbbda0
 	go.opentelemetry.io/collector/pdata v1.57.0
 	go.opentelemetry.io/collector/pdata/pprofile v0.151.0
 	go.opentelemetry.io/collector/pdata/xpdata v0.151.0