Rename "master" to "main". (#31050)

.github/CONTRIBUTING.md

@@ -65,7 +65,7 @@ Guidelines for bug reports:
    reported.
 
 2. **Check if the issue has been fixed** — try to reproduce it using the
-   latest `master` or development branch in the repository.
+   latest `main` (or `v4-dev` branch if the issue is about v4) in the repository.
 
 3. **Isolate the problem** — ideally create a [reduced test
    case](https://css-tricks.com/reduced-test-cases/) and a live example.
@@ -134,12 +134,12 @@ project (indentation, accurate comments, etc.) and any other requirements
 
 **Do not edit `bootstrap.css`, or `bootstrap.js`
 directly!** Those files are automatically generated. You should edit the
-source files in [`/bootstrap/scss/`](https://github.com/twbs/bootstrap/tree/master/scss)
-and/or [`/bootstrap/js/src/`](https://github.com/twbs/bootstrap/tree/master/js/src) instead.
+source files in [`/bootstrap/scss/`](https://github.com/twbs/bootstrap/tree/main/scss)
+and/or [`/bootstrap/js/src/`](https://github.com/twbs/bootstrap/tree/main/js/src) instead.
 
 Similarly, when contributing to Bootstrap's documentation, you should edit the
 documentation source files in
-[the `/bootstrap/site/content/docs/` directory of the `master` branch](https://github.com/twbs/bootstrap/tree/master/site/content/docs).
+[the `/bootstrap/site/content/docs/` directory of the `main` branch](https://github.com/twbs/bootstrap/tree/main/site/content/docs).
 **Do not edit the `gh-pages` branch.** That branch is generated from the
 documentation source files and is managed separately by the Bootstrap Core Team.
 
@@ -161,8 +161,8 @@ included in the project:
 2. If you cloned a while ago, get the latest changes from upstream:
 
    ```bash
-   git checkout master
-   git pull upstream master
+   git checkout main
+   git pull upstream main
    ```
 
 3. Create a new topic branch (off the main project development branch) to
@@ -181,7 +181,7 @@ included in the project:
 5. Locally merge (or rebase) the upstream development branch into your topic branch:
 
    ```bash
-   git pull [--rebase] upstream master
+   git pull [--rebase] upstream main
    ```
 
 6. Push your topic branch up to your fork:
@@ -191,7 +191,7 @@ included in the project:
    ```
 
 7. [Open a Pull Request](https://help.github.com/articles/about-pull-requests/)
-    with a clear title and description against the `master` branch.
+    with a clear title and description against the `main` branch.
 
 **IMPORTANT**: By submitting a patch, you agree to allow the project owners to
 license your work under the terms of the [MIT License](../LICENSE) (if it

.github/ISSUE_TEMPLATE/bug_report.md

@@ -8,7 +8,7 @@ Before opening:
 
 - [Search for duplicate or closed issues](https://github.com/twbs/bootstrap/issues?utf8=%E2%9C%93&q=is%3Aissue)
 - [Validate](https://html5.validator.nu/) any HTML to avoid common problems
-- Read the [contributing guidelines](https://github.com/twbs/bootstrap/blob/master/.github/CONTRIBUTING.md)
+- Read the [contributing guidelines](https://github.com/twbs/bootstrap/blob/main/.github/CONTRIBUTING.md)
 
 Bug reports must include:
 

.github/ISSUE_TEMPLATE/feature_request.md

@@ -7,7 +7,7 @@ about: Suggest an idea for a new feature in Bootstrap.
 Before opening:
 
 - [Search for duplicate or closed issues](https://github.com/twbs/bootstrap/issues?utf8=%E2%9C%93&q=is%3Aissue)
-- Read the [contributing guidelines](https://github.com/twbs/bootstrap/blob/master/.github/CONTRIBUTING.md)
+- Read the [contributing guidelines](https://github.com/twbs/bootstrap/blob/main/.github/CONTRIBUTING.md)
 
 Feature requests must include:
 

.github/workflows/release-notes.yml

@@ -3,7 +3,7 @@ name: Release notes
 on:
   push:
     branches:
-      - master
+      - main
 
 jobs:
   update_release_draft: