[fix](ci) Accept a hyphen in the PR title, and stop ignoring .github (#67491)

### What problem does this PR solve?

Issue Number: close #xxx

Related PR: #66957 (introduced the title-checker regression), #67487 (a
PR currently blocked by it)

Problem Summary:

Two independent bugs in the repository's `.github` tooling, both of
which make it easy to get a PR wrong for reasons unrelated to its
content.

---

#### 1. The PR title checker rejects any hyphen in the type or scope

```
[fix](arrow-flight) ...
[feature](inverted-index) ...
[improvement](github-actions) ...
```

**88 of the last 1500 commits on master use such a title**, including
#66957 itself — the change that introduced the current check. Its own
title, `[improvement](github-actions) Reduce redundant GitHub Actions
runs and checkouts`, would not pass the checker it added.

**Root cause.** #66957 replaced the `deepakputhraya/action-pr-title`
action with an inline `grep -qE` and kept the action's regex verbatim,
with the comment "Same regex as the previously used ... submodule". But
that action is **JavaScript**, where `\-` inside a character class is a
valid escape for a literal hyphen. **POSIX ERE has no such escape** — a
backslash inside a bracket expression is just a backslash. So

```
[a-zA-Z0-9 \-_]
```

does not mean "letters, digits, space, hyphen, underscore". It makes `\`
a member and then reads `-_` as a range endpoint, which leaves the
hyphen itself out of the set. Porting the pattern from JS to `grep`
silently changed its meaning.

The fix puts the literal hyphen last in the bracket expression, which is
how POSIX spells it:

```diff
-if ! grep -qE '\[([a-zA-Z0-9 \-_])+\]\(([a-zA-Z0-9 \-_])+\)(.*)' <<< "${TITLE}"; then
+if ! grep -qE '\[([a-zA-Z0-9 _-])+\]\(([a-zA-Z0-9 _-])+\)(.*)' <<< "${TITLE}"; then
```

A comment now records why the JS form cannot be restored verbatim, so
the pattern is not "fixed back" later.

#### 2. `.gitignore` ignores `.github`

`.gitignore` has had a bare `.github` entry under its `# other` section
since 9b5a4645b3 (`[Feature][external catalog/lakesoul] support
lakesoul catalog`, #32164) — a change that otherwise has nothing to do
with CI and touched only those two `.gitignore` lines, so it looks
accidental.

The existing files under `.github` survived only because they were
already tracked when the entry was added; `.gitignore` does not affect
tracked files. The entry therefore has no useful effect today, and two
harmful ones:

* Any **new** file under `.github` — a workflow, an action,
`CODEOWNERS`, an issue template — is silently ignored. `git status` does
not list it and `git add` refuses it without `-f`, so it is easy to open
a PR that is missing it.
* Even for a **tracked** file, `git add .github/workflows/foo.yml`
prints `The following paths are ignored by one of your .gitignore files`
and exits non-zero, which breaks `git add ... && git commit ...` in
scripts. This happened while preparing this very PR.

```
$ git check-ignore -v --no-index .github/workflows/new-thing.yml
.gitignore:155:.github    .github/workflows/new-thing.yml
```

.github/workflows/title-checker.yml

@@ -42,8 +42,12 @@ jobs:
             echo "::error::Unable to read the pull request title from the event payload."
             exit 1
           fi
-          # Same regex as the previously used deepakputhraya/action-pr-title submodule.
-          if ! grep -qE '\[([a-zA-Z0-9 \-_])+\]\(([a-zA-Z0-9 \-_])+\)(.*)' <<< "${TITLE}"; then
+          # Same character set as the previously used deepakputhraya/action-pr-title submodule,
+          # rewritten for POSIX ERE: that action was JavaScript, where '\-' inside a bracket
+          # expression escapes a literal hyphen. POSIX has no such escape -- a backslash there is
+          # just a backslash -- so '[a-zA-Z0-9 \-_]' made '\' a member and '-_' a range, dropping
+          # the hyphen itself. A literal hyphen has to be last in the bracket expression instead.
+          if ! grep -qE '\[([a-zA-Z0-9 _-])+\]\(([a-zA-Z0-9 _-])+\)(.*)' <<< "${TITLE}"; then
             echo "::error::PR title \"${TITLE}\" does not match the required pattern: [type](scope) description"
             gh pr comment "${PR_NUM}" --body "PR title \`${TITLE}\` does not match the required pattern: \`[type](scope) description\`"
             exit 1

.gitignore

@@ -152,7 +152,6 @@ docker/runtime/be/resource/apache-doris/
 
 # other
 compile_commands.json
-.github
 
 # generated kuromoji dictionary binaries
 /be/dict/kuromoji/*.bin