[INFRA] Prevent Actions workflows from running on people's forks (#3900)

* Prevent CI workflows from running on forks

* Leave for short workflows

* Update .github/workflows/isort.yml

* Missed some in testing.yml

---------

Co-authored-by: Remi Gau <remi_gau@hotmail.com>

.github/workflows/build-docs.yml

@@ -20,6 +20,7 @@ jobs:
   # Make citation metadata from CITATION.cff is valid.
   # as it is used in the documentation build.
     validate_cff:
+        if: github.repository == 'nilearn/nilearn'
         runs-on: ubuntu-latest
         steps:
         -   uses: actions/checkout@v3

.github/workflows/detect_test_pollution.yml

@@ -32,6 +32,8 @@ jobs:
 
     latest:
 
+        if: github.repository == 'nilearn/nilearn'
+
         runs-on: ubuntu-latest
 
         steps:

.github/workflows/testing.yml

@@ -11,6 +11,7 @@ on:
 
 jobs:
     min_requirements:
+        if: github.repository == 'nilearn/nilearn'
         runs-on: ubuntu-20.04
         name: Python 3.7, minimal requirements without Matplotlib
         defaults:
@@ -41,6 +42,7 @@ jobs:
             name: Upload coverage to CodeCov
 
     min_requirements_matplotlib:
+        if: github.repository == 'nilearn/nilearn'
         runs-on: ubuntu-20.04
         name: Python 3.7, minimal requirements with Matplotlib
         defaults:
@@ -69,6 +71,7 @@ jobs:
             name: Run tests
 
     latest:
+        if: github.repository == 'nilearn/nilearn'
         runs-on: ${{ matrix.os }}
         strategy:
             fail-fast: false
@@ -107,6 +110,7 @@ jobs:
             name: Upload coverage to CodeCov
 
     prerelease:
+        if: github.repository == 'nilearn/nilearn'
         runs-on: ${{ matrix.os }}
         strategy:
             fail-fast: false

.github/workflows/testing_install.yml

@@ -15,6 +15,7 @@ concurrency:
 
 jobs:
     test_install:
+        if: github.repository == 'nilearn/nilearn'
         runs-on: ${{ matrix.os }}
         strategy:
             fail-fast: false

.github/workflows/update_authors.yml

@@ -13,6 +13,7 @@ concurrency:
 
 jobs:
     update_authors:
+        if: github.repository == 'nilearn/nilearn'
         runs-on: ubuntu-latest
         steps:
         -   uses: actions/checkout@v3