fix(ci): repair yaml-path validation regex in _update-helm (#11)

The regex was '^\.[a-zA-Z0-9_.\[\]\"'\''-]+$' (single quote inside the
character class). Bash sees the lone ' as the start of a quoted
string, never finds a matching close, and aborts the script:

  /home/runner/.../11c37765-eb1d-4999-8298-6e83176c2ab2.sh: line 8:
  unexpected EOF while looking for matching `''
  Process completed with exit code 2.

Bug surfaced on release run 25112483893 — the first time Update Helm
actually executed end-to-end. Earlier runs either OOMed or used a
manual helm-charts PR (blockscout#177) so the broken script never ran.

Two issues, one fix:

1. Drop the lone single quote from the class. yq paths we use
   (.frontend.image.tag, .image.tag) never contain single quotes;
   stripping the apostrophe is safe.

2. Use the POSIX bracket-expression idiom for including literal
   square brackets: ']' must come first inside [], '[' anywhere
   else. The form '\[\]' worked in some regex flavors but breaks
   bash's =~ pattern matching. Verified locally that the new form
   '^\.[][a-zA-Z0-9_.-]+$' accepts .frontend.image.tag,
   .image.tag, .foo[0].bar, and rejects the obvious injection
   shapes (semicolons, dollar signs, spaces, backticks, pipes).

Author: alexandre-parfin

.github/workflows/_update-helm.yml

@@ -124,8 +124,12 @@ jobs:
             exit 1
           fi
 
-          # Validate yaml path: must start with '.' and contain only letters, digits, dots, underscores, hyphens, brackets, quotes
-          if ! [[ "$YAML_PATH" =~ ^\.[a-zA-Z0-9_.\[\]\"'-]+$ ]]; then
+          # Validate yaml path: must start with a dot and contain only letters,
+          # digits, dots, underscores, hyphens, and brackets. POSIX bracket-class
+          # form requires ']' first and '[' later to be treated as literals
+          # ('^\.[][a-zA-Z0-9_.-]+$'); a lone single-quote in the class would
+          # break the bash lexer.
+          if ! [[ "$YAML_PATH" =~ ^\.[][a-zA-Z0-9_.-]+$ ]]; then
             echo "❌ Invalid yaml path: $YAML_PATH"
             exit 1
           fi