ci: add labels for GitHub Actions dependabot updates

[Ayushmore1214]

What this PR does: Adds labels for GitHub Actions Dependabot pull requests in .github/dependabot.yml.

Why we need it:

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[Ayushmore1214]

@Warashi PTAL!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 29.38%. Comparing base (dcc037e) to head (fd73c2c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6906   +/-   ##
=======================================
  Coverage   29.38%   29.38%           
=======================================
  Files         601      601           
  Lines       64278    64278           
=======================================
  Hits        18886    18886           
  Misses      43924    43924           
  Partials     1468     1468           

Flag	Coverage Δ
.	23.15% <ø> (ø)
.-pkg-app-pipedv1-plugin-analysis	32.43% <ø> (ø)
.-pkg-app-pipedv1-plugin-ecs	31.74% <ø> (ø)
.-pkg-app-pipedv1-plugin-kubernetes	58.37% <ø> (ø)
.-pkg-app-pipedv1-plugin-kubernetes_multicluster	59.66% <ø> (ø)
.-pkg-app-pipedv1-plugin-scriptrun	54.83% <ø> (ø)
.-pkg-app-pipedv1-plugin-terraform	38.18% <ø> (ø)
.-pkg-app-pipedv1-plugin-wait	33.04% <ø> (ø)
.-pkg-app-pipedv1-plugin-waitapproval	52.71% <ø> (ø)
.-pkg-plugin-sdk	50.34% <ø> (ø)
.-tool-actions-gh-release	19.23% <ø> (ø)
.-tool-actions-plan-preview	25.51% <ø> (ø)
.-tool-codegen-protoc-gen-auth	0.00% <ø> (ø)

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[Warashi]

dependabot automatically adds labels to PRs like the one below.
Warashi/cage#76

Additionally, we manage PR labels with labeler, so we don't have to configure them in Dependabot.

pipecd/.github/labeler.yaml

Lines 11 to 16 in dcc037e

	area/build:
	- hack/*
	- .github/*
	- .github/**/*
	- Makefile
	- local/*