chore: make some gh workflows only run on jdx/mise (#2489)

Cron scheduled and jobs that require credentials are not scheduled on
any fork.

The test-plugins job is still requestable by hand on forks.

.github/workflows/docs.yml

@@ -21,6 +21,7 @@ env:
 
 jobs:
   release:
+    if: github.repository == 'jdx/mise'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4

.github/workflows/release-plz.yml

@@ -20,6 +20,7 @@ env:
 
 jobs:
   release-plz:
+    if: github.repository == 'jdx/mise'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4

.github/workflows/test-plugins.yml

@@ -20,6 +20,9 @@ env:
 
 jobs:
   build-linux:
+    if: >
+      github.event_name == 'workflow_dispatch'
+      || github.repository == 'jdx/mise'
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4