triage: add labels for boost, icu4c, ffmpeg dependents (#105002)

We often struggle with merging boost and icu4c updates due to merge
conflicts. The same occasionally happens with ffmpeg updates.

Let's make it easier to identify PRs that could potentially cause merge
conflicts with appropriate labels.

Author: carlocab

.github/workflows/triage.yml

@@ -73,6 +73,14 @@ jobs:
               path: Formula/.+
               content: license .*"(GPL|LGPL|AGPL|GFDL)-[0-9].[0-9][+]?".*
 
+            - label: boost
+              path: Formula/.+
+              content: depends_on "boost(@[0-9.]+)?"
+
+            - label: ffmpeg
+              path: Formula/.+
+              content: depends_on "ffmpeg(@[0-9.]+)?"
+
             - label: go
               path: Formula/.+
               content: depends_on "go(@[0-9.]+)?"
@@ -81,6 +89,10 @@ jobs:
               path: Formula/.+
               content: depends_on "(ghc|haskell-stack)(@[0-9.]+)?"
 
+            - label: icu4c
+              path: Formula/.+
+              content: depends_on "icu4c(@[0-9.]+)?"
+
             - label: java
               path: Formula/.+
               content: depends_on "openjdk(@[0-9.]+)?"