Attempt to fix release (#1368)

The v1.3.1 release failed to make it all the way through; [goreleaser
was pinned to an old version of
Go](https://github.com/bufbuild/protoc-gen-validate/actions/runs/22144192935/job/64016483091),
and the [Dockerfile failed to build for the python
release](https://github.com/bufbuild/protoc-gen-validate/actions/runs/22144192900/job/64016483115#step:5:278).

From Claude:

```
⏺ The problem is clear. The Dockerfile uses ubuntu:focal (Ubuntu 20.04), which reached End of Life on April 2, 2025. The python3.10 and python3.10-venv packages were backported to focal
  during its active LTS period but are no longer available in the focal apt repositories after EOL.

  The fix is to update the base image to ubuntu:jammy (22.04 LTS), which has Python 3.10 natively. The only other required change is openjdk-8-jdk → openjdk-11-jdk since Java 8 isn't in
  jammy's repos.
```

Seemed reasonable to me, and confirmed `docker build -t
protoc-gen-validate:test .` works.

Author: stefanvanburen

.github/workflows/goreleaser.yaml

@@ -18,7 +18,7 @@ jobs:
           fetch-depth: 0
       - uses: actions/setup-go@v6
         with:
-          go-version: 1.21.x
+          go-version-file: 'go.mod'
       - uses: goreleaser/goreleaser-action@v6
         with:
           distribution: goreleaser

Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:focal
+FROM ubuntu:jammy
 
 ENV DEBIAN_FRONTEND=noninteractive
 # apt packages
@@ -17,7 +17,7 @@ ENV INSTALL_DEPS \
   python3-pip \
   apt-transport-https \
   curl \
-  openjdk-8-jdk \
+  openjdk-11-jdk \
   gnupg
 
 RUN apt update \